Neutrino Blog

A T2K Neutrino Journey

2012-02-07T16:50:00.000Z

With all the talk of faster than light neutrinos I remembered something I wrote for my website but have never posted as a blog post; well here it is with added faster than light calculation and conclusion.

How long does it take to get from J-PARC, where the beam of neutrinos are created, to the Kamioka mine, home of the Super-Kamiokande far detector in the T2K experiment? Below are a few options...

Public Transport...

Google maps predicts that, despite the brilliant Japanese public transport system, it would require a traveller to take a one hour walk and a total of five different trains!

Journey time: 7 hours

View Larger Map

By Car...

Google maps suggest a drive which takes in a lot of views en-route. After tackling central Tokyo the route takes the driver past KEK, Japans premier particle physics laboratory until the building of J-PARC, where there are still many particle physics experiments taking place and planned in future. The route proceeds to take the driver through the outskirts of Fuji National Park, where one should get great views of Mount Fuji on a clear day. After a long drive through rural Japan we eventually reach Japans western mountain range and the end of our journey.

Journey time: 7 hours and 29 mins

View Larger Map

By Neutrino...

Not a very plausible form of transport for Humans, but if we could travel on or alongside the neutrino then the journey would be a whole lot quicker! The neutrino is an extremely light particle, with a mass of the order of 1eV which is equivalent to just 1.78 x 10^-36 kg, 500,000 time lighter than an electron! This extremely small mass allows a neutrino with relatively small energy to travel at almost the speed of light, the fastest speed possible in the universe.

The neutrino is also the most ghostly of particles, interacting only by what is know as the weak nuclear force. This is the force which is responsible for much of the nuclear decay we see in large atoms such as Uranium and Plutonium. The key thing is that it’s name doesn’t lie, this force is feeble, in fact it is 100 billion times weaker than the electromagnetic force which determines the chemistry of everything around us. This all means that the neutrino interacts with regular matter, such as the earth through which it travels between J-PARC and Super-K, extremely rarely. In fact the average distance that a neutrino travels before interacting is measured in light years of lead; that’s lead blocks of the order 10¹⁶m and more! Because of this the neutrino obviously travels in a straight line between J-PARC and Super-K as it does not interact as our other travelers do, such as changing trains or getting stuck in traffic.

If we couple the speed with the direct line of travel you get a much quicker journey time.

Journey time: Less than 1 miilisecond (that’s 1/1000 of a second)

distance, d = 295 km; speed of light, c = 299792458 m /s; time, t = d / c ~ 0.984 x 10^-3 s

Because of this fast journey time we need a fast way of telling the Super-K detector that neutrinos are being fired its way, and this is done using GPS signalling - similar to the GPS found in you Sat-Nav system in your car. The times at which the neutrino beam is fired, and the time at which neutrinos are seen in Super-K, are measured in Universal time by receiving signals from GPS satellites .

Recently there has been a suggestion in results from the OPERA experiment that neutrinos may travel faster than light. If we take the value suggested in their paper then the difference in travel time between calculated above would be 24.4 nanoseconds (1/1000,000,000 of a second). To try and see this tiny time difference there are plans in the pipeline to upgrade the timing systems currently installed on the T2K experiment (and also the MINOS experiment in the US). These upgrades should be performed within the next year but the ghostly nature of the neutrino will mean that we will not have a definitive answer for a few years yet... watch this space!

From Tokai to Kamioka Once More!

2012-01-28T09:05:00.000Z

After the earthquake which hit the East coast of Japan in March of last year the Tokai to Kamioka (T2K) experiment was taken out of action. But, with the hard work and determination of many scientists and engineers, just 10 months on it is almost back to 100% operation and raring to go.

The J-PARC Proton Accelerator, courtesy of KEK.

Many aspects of the experiment that had to be repaired or rebuilt; the largest and most complex element was the proton particle accelerator (pictured left), used to produce the beam of neutrinos. Magnets, used to accelerate and bend the protons in their circular path, had to be aligned together with millimetre accuracy. These protons then had to be focused, with even greater accuracy to hit a target and produce neutrinos (more info here). Months of tweaking and fixing and we now have protons producing neutrinos.

Then there were the detectors, the machines that actually looked for the neutrinos. Because the neutrinos were being fired such a massive distance of 295 km to the West the very far detector, Super-Kamiokande, was unscathed by the earthquake. The collection of near detectors (pictured below) were, however a great deal closer at just 280m from the start of the neutrino beam, on the same site as the particle accelerator. Again the effort of many engineers and scientists has resulted in the successful restart of these huge neutrino cameras.

The ND280 near detector of the T2K experiment.

The last piece of the puzzle is the massive bell-like magnetic horns that focus the neutrino beam and removes unwanted anti-neutrinos. Here it is a case of repairing power supplies that provide a massive 250kA of electricity in nanosecond pulses to generate massive magnetic fields. Despite the lack of focus in the beam at both the near and far detectors in the experiment have seen neutrinos! - see below. Although these sightings will not be used for physics they are a very positive sign that T2K is back. Data taking for physics will begin in March 2012 and it won't be long before it starts to excite the community once again with new results.

Below I show and example of the neutrinos we have seen this month in the ND280 near neutrino detector, also shown is the one fully contained event seen by the Super-Kamiokande far detector.

A neutrino event in the near detector.
Courtesy of the T2K ND280 collaboration.

A fully contained neutrino event in the Super-Kamiokande detector.
Event display courtesy of Kamioka Observatory, ICRR, University of Tokyo

Weak Booom!

2011-10-01T09:03:00.000+01:00

Of the large amount of papers that are being put forward for debunking faster than light neutrinos one in particular caught my eye. On Thursday a paper by Andrew G. Cohen and Sheldon L. Glashow about faster than light neutrinos losing energy rapidly and not making the 730km at superluminal speed. This post pulls together a lot of threads and I link to previous posts in the text to provide the relevant background.

Electromagnetic field

The fundamental forces, the rule book for they way the Nature interacts with itself, are communicated to the Universe via things called fields. A good visual example of a field is putting iron filings near a bar magnet - this is the electromagnetic force field made visible. Every particle with an electric charge, e.g. the electron, emits a similar electromagnetic field. These force fields move at the speed limit of the universe - the speed of light. If the speed of light is slowed down, as it is in water or glass, then it is not against the laws of Nature for charged particles to out run light. If this is the case then the charged particles produce flashes of light known as Cherenkov radiation which takes energy away from the particle until it's speed is less than light in water (or some other medium). For more info on Cherenkov light please read this previous post.

Neutrinos are ghostly as I have said many times and interact rarely with the Universe. On the rare occasion they do interact it is via the weak nuclear force. Because the neutrino feels this weak force, Cohen and Glashow put forward the argument that neutrinos would lose energy by a similar process to Cherenkov radiation. Instead of a burst of light however you would get a burst of weak force. Particles of light, photons, are the force carriers of the electromagnetic force and are the things released in Cherenkov radiation. The Z⁰ weak force carrier is essentially just a heavy version of the photon and it is this that is released in the burst of weak force.

The weak force carriers can't live out in the real world for too long, due their heavy size they are unstable. They quickly die and give birth to matter and anti-matter. When Z⁰ dies it can produce pairs of electron and antielectron (positron)^(a). In this process the neutrino loses energy until it reaches a lower limit (terminal energy) of about 12.5GeV. The OPERA experiment has however seen neutrinos with energy above this - with average energy about 17.5GeV. Quoting the paper "...observation of neutrinos with energies in excess of 12.5 GeV cannot be reconciled with the claimed superluminal neutrino velocity measurement."

(a) The Z0 can also produce neutrino-antineutrino pairs, but the energy constraint here is less marked. Neutrinos can also lose energy by emitting light as well through a complicated self interation of the other weak force carriers the W± but this process is also not too important for this discussion.

Supernova Neutrinos in 1983 and 1987?

2011-09-30T07:00:00.000+01:00

NOT a good neutrino detector

Take a look at your thumbnail. This is not some mind game, go on just look. Every second there are over 100 billion neutrinos passing through an area about the size of your thumbnail (~1cm²). They pass straight through and continue on their long and lonely cosmic journey. There are trillions passing through your body right now as you read this. But in your lifetime you would be lucky if a single neutrino even noticed you existed, or visa versa. Don't be offended, they are not ignoring you. The neutrino is the shyest of the shy, interacting with the Universe around it on only the rarest of occasions.

It is possible however for us to catch a rare glimpse of one of these ghostly particles. To increase our chances of seeing a neutrino we require as large an amount of stuff as possible; the more stuff you put in the way of neutrinos the more likely that one will notice it. Massive neutrino detectors are constructed deep underground to shield from other particles coming from cosmic ray interactions the atmosphere. Three massive neutrino detectors saw antineutrinos from SN1987a; the Baksan Underground Scintillation Telescope (Baksan) in Russia, the Irvine Michigan Brookhaven (IMB) detector in the US and KamiokaNDE in Japan.

KamiokaNDE - a much better neutrino detector

Kamiokande, in its second incarnation in 1987, tried to catch a neutrino in it massive tank of 3000 tonnes of ultra pure water (over 42,000 human bodies worth). Even with all of this stuff in the way Kamiokande II saw around 6 of the trillions upon trillions of neutrinos that passed through it everyday. Imagine their surprise then, when asked by optical astronomers to check their data on 23rd February 1987, they saw a spike of 12 neutrinos in just 12.4 seconds! The spike in number of neutrinos seen was also experienced by the IMB and Baksan experiments who saw 8 and 5 neutrinos each in the same short time (see the graph below). With so many neutrinos seen in such a short space of time there must have been a huge intensity of neutrinos passing through the Earth (10⁵⁷-10⁵⁸ neutrinos released in total by the supernova over the few seconds), far greater than that from the Sun and atmosphere combined.

Intensity of neutrinos equates to intensity of energy, as it is the neutrinos that take energy away from the supernova. The intensity of neutrinos and energy was calculated and found to agree well with theoretical models. In these models the energy taken away from supernova accounts for 99% of the total energy emitted. The energy released in forming a neutron star comes primarily from essentially the difference in mass between the normal core and the new neutron star. This is a value that is well constrained. So I argue that if the intensity of neutrinos see just hours before SN1987a accounts for 99% of the theoretically modeled energy released, then there could not have been neutrinos missed 4.14 ±1 years previous.


The SN1987a neutrinos seen. Energy and time since first neutrino.

Of the three neutrino observatories that saw antineutrinos from SN1987a, only the IMB and Baksan detectors were active in 1983, both of started operation in 1982. Kamiokande in Japan, was the largest of the three but did not begin operation until the second quarter of 1983. As far as I am aware there was no neutrino spike such as that seen in 1987 - after this detection of a supernova in neutrinos was made all historical data was scrutinised and nothing appears in publication.

The neutrinos seen by these detectors were electron antineutrinos. The reason for this is that the likelihood for electron antineutrinos to interact with the normal stuff around us is far far higher because they have the possibility to interact by inverse beta decay p + anti-ν_e → n + e⁺. One could then make the argument that perhaps the other types of neutrino traveled faster than light and then we missed them 4 years previous because we did not see them. For this argument I point you toward my post on neutrino type.

Not Feeling Very Energetic

2011-09-28T15:29:00.000+01:00

As people have pointed out the neutrinos released in supernova deaths of stars, such as SN1987a, a far less energetic than the neutrino beam used by the OPERA experiment. The energy of neutrinos fired from CERN to the OPERA detector in Gran Sasso, Italy, are of the order 1000 times as energetic as those seen from SN1987a.

Old physics: AKA Our Current Understanding of the Universe

Einstein's theory of relativity assumes that nothing can travel faster than the speed of light, this property is known as Lorentz invariance. It is hard coded into the mathematics and it is the ratio of the squares of the mass and energy that determines how close to the speed of light a particle can travel. The smaller the ratio m²/E² the closer to the speed of light a particle gets^(a).

The extremely small mass of the neutrino, the current upper limit is 2eV/c^{2 (b)}[1], means that it requires very little energy to travel at amazingly fast speeds. At an energy of 10 of MeV, neutrinos are traveling at 99.999999999998% the speed of light. The difference in speed when we raise the energy of the neutrino to 10GeV is a tiny 0.00000000001998%. If 10MeV (roughly that from SN1987a) and 10GeV (roughly the energy of OPERA) neutrinos were in a race all the way from the large Magellanic cloud, where SN1987a died spectacularly, then the 10GeV neutrinos would arrive just one tenth (0.1) of a second before the 10MeV energy neutrinos. Although the OPERA energy neutrinos would be faster, note that because of Lorentz invariance they would not travel faster than light.

New Physics: AKA Pastures New

The land of theories, where new physics lives.

The only way in which this can explain faster than light neutrinos would be if a new physics, beyond our current understanding, 'switches on' at high previously unexplored energies. 'Switches on' is a phrase that theorists like. New physics may exist at scales of energy over the horizon of our previous experiences as it is in these lands that theories lie. The GeV energies used by the OPERA is indeed a new frontier in our understanding of the neutrino.

I explain in the addendum to my original blog post on this subject that the forerunner of theories which allow the neutrino to travel faster than light is that of quantum gravity[2]. Here the neutrinos interact differently than light does with the backdrop of the Universe, the foamy space-time, upon which Nature in played out. This difference in interaction, effectively particles of light - photons - and neutrinos traveling through different subsets of extra dimensions.

I would not claim any great knowledge in quantum gravity but I understand that as yet there is no evidence for extra dimensions or the quantum space-time foam talked of. Who knows, if the OPERA results do withstand the rigorous tests and scrutiny they will most certainly be under then it may be the first hint of quantum gravity. Only time, repeat results, and a lot of hard work will tell.

Next post I hope to cover the fact that neutrinos might have indeed passed through the Earth 4 years before SN1987a was seen in light.

Footnotes

(a) It is this ratio that shows us any particle with a (real finite) mass requires infinite energy to reach the speed of light because it is the only way the ratio can get to zero: m / ∞=0

(b) eV or electron volts are a measure of energy of the very small. It is the amount of energy you would give an electron particle if you were to accelerate it across an electric potential of one Volt (more info on Wikipedia). From Einstein's E=mc² equation we can relate energy and mass and we do so with the units of mass for particles, so we can express small masses in units of eV/c².

References

[1] Particle Data Group (PDG) 2011: Neutrino Data

[2] Probes of Lorentz Violation in Neutrino Propagation; John Ellis, Nicholas Harries, Anselmo Meregaglia, André Rubbia and Alexander S. Sakharov

Supernovas and Neutrino Types

2011-09-27T09:43:00.001+01:00

A Supernova is like a cup of tea...

There has been lots of talk about my previous post so I would like to follow up with some more comments about Supernova neutrinos. This post covers the comments that the difference between the supernova example I blogged about and OPERA experiment is due to the fact they they are dealing with different types of neutrino.

It is true, the neutrinos seen from a supernova such as SN1987a are a different type (technical term is flavour) to that used in OPERA. The difference type cannot, however, be account for the reason we see one type of neutrino traveling faster than the speed of light and not another. I can say this with confidence because neutrinos don't travel as their types but instead as a mixture of different masses. Each type of neutrino is a different admixture of the same three states of neutrino mass. Because of this the different types of neutrino are inexorably linked - one cannot travel faster than the speed of light with out the other also having the ability to do so. Want to know more about the types of neutrino emitted by a supernova? Then read on...

As the core of a supernova collapses (section 1 in the graph below) electrons in atoms are forced to combine with protons - this is called 'neutronification'. The products of this process are neutrons, which form the remnant neutron star, and electron neutrinos. This process takes just a few microseconds produces a sharp pulse (section 2 in the graph). The energy of these neutrinos however were too low for the 1987 neutrino observatories to see.

e + p → n + ν_e

Neutronification (my word of the week!)

The intensity of different types of neutrino as a function of time after collapse.

Instead the neutrino observatories saw higher energy neutrinos coming from a longer process called neutrino cooling (sections 3&4 of the graph), which took place over ~10s. When the neutron star forms it is warmer than the surrounding space and cools down to this temperature by emitting radiation; like a cup of tea cooling to room temperature. The radiation from the neutron star however is not light, infrared heat, as in the case of the cup of tea but is instead neutrinos. All types of neutrino; electron, muon and tau, neutrinos and antineutrinos are produced in massive amounts. As they escape they take energy away with them, cooling the neutron star.

It is a small subset of these cooling neutrinos that the neutrino observatories saw in 1987. Because of the probability of interaction (something particle physicists call 'cross-section') that the neutrino observatories saw almost all electron antineutrinos (and possibly one electron neutrino). The process that turns one electron antineutrino and a proton into a neutron and a positron (anti-electron), is millions of times more likely than any of the ways in which the other types of neutrino and antineutrino interact. So although all types of neutrino were produced in the neutrino cooling, we only had the opportunity to see electron antineutrinos.

I'll try to post again soon covering the difference in energy of the two sets of neutrinos.

Arriving Fashionably Late for the Party

2011-09-23T03:54:00.006+01:00

Just a quick post to talk about the latest paper released by the Opera experiment [1] which presents results of neutrinos traveling faster than light in a vacuum. While the debate on systematic errors is going to be a long one I just wanted to play around with some of the number quoted in the paper and relate this to results from an independent neutrino source - a supernova death of a star. Namely supernova (SN) 1987a.

The optical after and before picture of SN1987a (c) AAO

This was the first supernova to been seen not only in visible light but also in neutrinos (please see this post for more on the neutrino signal seen). The difference between seeing neutrinos and the light from the supernova was ~3hours - seen by comparing neutrino observatory and telescope data. We now understand this difference as the journey of the light being impeded by the atmosphere surrounding the dying star.

If the faster than light claim of the Opera paper [1] were to be accepted, as a six standard deviation result would imply, then the difference should have been much much greater. The paper quotes a fractional difference between neutrino speed and that of light of

(v-c)/c = δt/(TOF_c - δt) = (2.48 ± 0.28 (stat.) ± 0.30 (sys.)) x 10^-5

Supernova 1987a was a distance of 166,912 ± 10000.1 light years [2] from Earth when it died. Taking these values we can calculate that the time difference between the neutrinos arriving at the neutrino observatories and the telescopes seeing SN1987a would be

2.48 x 10^-5 x 166912 = 4.14 years

Combining the errors on the SN1987a distance, systematic and statistical errors of the Opera result we get a value of

4.14 ± 1 years

There is no evidence to support that this is the case - as I mentioned the neutrinos were seen just 3 hours before SN1987a was seen by optical telescopes. In this case the neutrinos did not arrive early for the party it was the light that was fashionably late!

*Addendum* There are of course loopholes to this argument, for instance there may be higher order quantum gravity effects which violate Lorentz invariance [3]. Either way the result will be hotly debated - is it an unknown systematic error or some exciting hint at new physics?

Follow up post about supernova and neutrino type.
Follow up post about the difference in neutrino energy.

[1] Measurement of the neutrino velocity with the OPERA detector in the CNGS beam; OPERA collaboration
[2] Properties of the SN 1987A circumstellar ring and the distance to the Large Magellanic Cloud, Panagia; N., Gilmozzi, R., Macchetto, F., Adorf, H.-M., & Kirshner, R. P.
[3] Probes of Lorentz Violation in Neutrino Propagation; John Ellis, Nicholas Harries, Anselmo Meregaglia, André Rubbia and Alexander S. Sakharov

CERN Press Release here

Coming At It From All Angles - Part 3

2011-07-04T16:29:00.000+01:00

In the previous post we found that we can describe how mixed up a neutrino is at birth using three numbers, or angles - and a fourth number which I will keep for a future post (I like to keep you hanging!). But what happens as a neutrino starts its journey through life?

A Life Less Ordinary

I briefly mentioned that it is the mixture of masses that determines how a neutrinos lives its life between birth and death, when it eventually interacts with the world. The behavior is dictated by a famous equation, which all physics majors will learn at University, the Schrödinger equation. In our system that we set up in the previous post the Schrödinger equation essentially dictates a path which the vector of the neutrino moves along. So a traveling neutrino is equivalent to a vector rotating around the zero point and drawing out a well defined path.

Example of an initial state of a neutrino at birth - pure electron like.

Example of an final state of a neutrino at some time greater than 0


How probable the neutrino is to choose each flavour.

So from its birth at t=0 the vector that represents the neutrinos state of being is constantly changing until at some time later, say t=t1, it interacts with the world around it. When the neutrino interacts it is again asked the question of what flavour it is - the probability of which it chooses is determined by projecting the vector onto the flavour axes. The probability is the square of this projection (amplitude). As soon as the neutrino decides it becomes a pure electron, muon or tau like neutrino and behaves as such. This phenomenon is also known technically as a collapse of the wave function of the neutrino - as it changes from a haze of probability to a billiard ball.

To figure out these probabilities experiments must wait patiently and look for many neutrinos. It is like measuring the probability of rolling a six on a dice by noting down the result of many rolls - but you can only roll the dice a few times a day in most cases.

The Passage of Time

The speed at which the neutrinos vector traces the defined path depends on the difference in mass between the three neutrinos masses. As I have mentioned in a previous post this is uniquely defined by just two numbers. The size of these numbers have been measured by monitoring the disappearance of electron neutrinos from the Sun (Δm₁₂) and muon neutrinos from the atmosphere (Δm₂₃).

The angle of initial mixture and the mass difference involved can be measured by looking at the probability of survival as a function of neutrino energy divided by the distance they have traveled. The position of the first dip in probability can tell us how quickly the neutrinos vector is spinning and therefore the Δm (in fact it is the Δm²). The size of the first dip let's us know how mixed up the neutrino was originally and therefore an angle of displacement between the mass and flavour axes.

Next: The Solar Neutrino Problem and Solution

Coming At It From All Angles - Part 2

2011-06-28T11:55:00.001+01:00

This is a continuation of a previous post. In this post we talk a little further in depth about the mathematics behind neutrino oscillation on a road to understanding the new exciting results released by the T2K experiment.

Particles and Vectors

So how do we describe the bizarre behaviour of neutrino in maths? It is all about rotation. My spatial awareness is not the best (I have dented cars to prove this!) but I am aware that we live three space dimensions (3D) - up-down, left-right and backwards and forwards. To chart a position in 3D space we can place a point on a graph with three axes, traditionally called x, y and z.

Fig. 1: Projection of a vector onto an axis

Instead of just a point imagine an arrow now pointing from the zero point (x=0,y=0,z=0) to another point in 3D space. This arrow has a direction and size - this is a vector. You can imagine a particle, like a neutrino, as a vector in a 3D space - not just a point but an arrow with a direction (the size of the particle vector is 1 in the following).

Instead of there being just one set of 3D axes you can have multiple sets all centered at the same zero point. Each of the sets of axes describes different properties of the particle, not a position in space. One set of axes can, instead of being x,y and z spacial dimension, describe the flavour of the particles - how electron-like, muon-like and tau-like the neutrino is. Another set of axes can describe the mass of the neutrino.

Measuring Properties

There is a limit on the size of the axes and therefore the size of the vector describing the particle in question - this is 1, or 100% if you like, because nothing can be more than 100% electron-like for example. Things can be less than 100% though - to find how much of each a particle is we need to project its vector onto each of the different axes.

Fig 2: A pure electron neutrino is a mix of different masses

What I mean by project is really like shining a light over the vector at the axis in question and measuring the size of the shadow it casts (Fig 1). If you have a stick that is 100cm (1m) long at some angle off the floor, shine a torch from above (or either side) and you will see that the length on the floor (or the walls) is less than 1. The probability of a vector being either of the properties is then calculated as the square of the shadow length it casts. Use the corner of a room as a zero point and imagine the floor and walls as you axes and try it for yourself - this is all we are doing but in maths.

Mixing It All Up

Although intuitively we associate definite mass to electrons and the like, there is no law in nature to say that a certain flavour of particle should have a definite mass. This is displayed best by the neutrino. In our model of 3D axes outlined above this would show itself as a misalignment, a rotation between the axes. If a neutrino is born as electron-like, i.e. with its vector lying along the electron axis, then one can see automatically that it is not a definite mass but instead a mixture of all three - the neutrino vector is non-zero on all three of the mass axes (Fig 2).

All Angular

Fig 3: Three angles describe the rotation between neutrino mass and flavour.

The misalignment of the mass and flavour axes can be uniquely defined by three angles of rotation (Fig 3). These angles, just numbers, cannot be predicted with the maths but instead must be measured through experiments. They are measured by looking at the changing flavours of neutrino from various different sources.

There is also one other number that has to be measured - one that essentially defines the difference in overall orientation of the axes for neutrinos and their antimatter version the antineutrinos. To understand the difference between matter and antimatter is to understand the creation of the Universe from the pure energy Big Bang - more about latter in this series.

Coming At It From All Angles - Part 1

2011-06-27T09:36:00.003+01:00

The T2K experiment has recently started a journey down an exciting path. With more data it is hoped that T2K will eventually lead us to an clearer understanding of an essential chapter in the creation story of the Universe - but what is the experiment actually measuring? In this series of posts I will talk about the bizarre behaviour of neutrinos, what experiments need to do to characterise this behaviour and how they may hold the key to creation.

I will cover a lot of information and link back to previous posts where I feel more information may help the reader but please do leave any questions in the comments.

A Definite Possibility

When you go to the smallest 'quantum' scales of Nature things become strange indeed. When things interact with each other they act as definite snooker/pool balls. But, between these interactions things become hazy, waves of possibilities and probabilities. It because of this hazy probability that neutrinos are given the opportunity to change their character when they travel.

All Mixed Up!

At the start of their life a neutrino knows definitely that they are electron-like, muon-like or tau-like what we call the different 'flavours' - this is because they are born in weak force interactions alongside these other particles. Ask the neutrino its mass however and it would not be certain - there is no law of Nature that states a certain flavour of particle should have a certain mass - so the neutrino is born knowing exactly what type of flavour of particle it is but not exactly what mass it has.

The way a particle travels is determined by their mass and energy (governed by the Schrödinger Equation). As the mixed up neutrino starts on it's journey into the big wide world, the mass confusion changes in a well defined mathematical way - the probability that it might be either of the three possible masses continually changes.

When Will I See You Again?

On the extremely rare occasion a neutrino decides to interact again with the outside world it must do so, as in its birth, via the weak force. Here it is faced with a choice of yet again being electron-like, muon-like or tau-like. How probable it is to choose either of these flavours depends on the mixture of its possible masses. Because the mixtures have changed during its lifetime there are now non-zero probabilities that the neutrino wants to be a different flavour to which it was born - it is uncertain of what flavour it is.

But choose it must. This is the reason neutrinos change their mind as to which weak flavour they are, electron, muon or tau. This process is called neutrino oscillation.

Part 2: The maths and numbers behind neutrino oscillation

Hello There Electron Neutrino

2011-06-15T11:09:00.006+01:00

A candidate electron like neutrino event in Super-K

After weeks of rumours, and reporters even contacting yours truly for the scoop, the latest results are finally in - The results released by the Tokai to Kamioka (T2K) experiment that is! Today T2K released results in seminars, a press release and the first physics paper to be released by the experiment - results that sent waves of excitement through the particle physics and larger community. But why?

The Results

Before the earthquake of March 11th the T2K created about 2% of the neutrinos it hopes to in the lifetime in the experiment and fired them in a beam at its particle detectors. A group of detectors just 280m from the creation point of the neutrinos tells us how many neutrinos of each type (muon or electron type) we are firing. The neutrinos then continue 295km to the Super Kamiokande (Super-K) detector where again the number of each type is determined.

The final cut, on neutrino energy,to select electron like
neutrino events.

T2K creates almost 100% Muon type neutrinos and hopes that because of the identity crisis neutrinos undergo some of these might decide to turn into electron neutrinos. With the small amount of data taken, 88 neutrinos were clearly seen in Super-K. After a number of cuts on various aspects of the data, 6 of these were determined to be be electron like. As I mentioned the beam of neutrinos fired is ALMOST 100% muon neutrinos so there is a small contamination of electron neutrinos. This, plus other particles that can mimic electron neutrinos, means that we were already expecting to see 1.5 background electron like events.

With 6 events seen and 1.5 expected we can say with 99.3% confidence that we have seen some of the muon neutrinos change into electron neutrinos. This is a strong hint and the first of its kind.

The Physics

The changing personality of the neutrino is a natural result of quantum mechanics. Neutrinos, as other fundamental particles are both a wave (when travelling) and a particle (when interacting). The wave like nature allows the probability that the neutrino is muon-like or electron-like to change as it travels from creation to detection. As it is a purely quantum mechanical effect we have well understood mathematics which describes the evolution of these probabilities.

If we are to understand the character of the neutrino there are six numbers that we have to measure from Nature to plug into the maths.

Two of these numbers determine how fast the neutrino can change its character. These are the difference in the mass of the three neutrino masses. These numbers determine where you place your detectors to see the character differences.

How mixed up is the neutrino at birth?
Some of the maths involved - just to scare you!

Three of these numbers determine how mixed up the neutrino is to start with (diagram above). Two of these numbers have been measured (red,blue), but still need to be accurately measured. The third and final number seems to be really small, so much so that it has until now been taken to be zero. It is this third number, which we call θ-13, that determines how many muon neutrinos decide to become electron neutrinos in the T2K experiment. So the fact that T2K sees electron neutrinos appearing from muon neutrinos gives a strong hint that this number is in fact greater than zero.

Finally there is one number which tells us how neutrinos (matter) and anti-neutrinos (anti-matter) differ in their character crisis. This final number is always found multiplied by the small number described above - so to measure the difference between matter and anti-matter this we need the small number to be greater than zero (anything x 0 = 0) and we then need to know this number. T2K hopes to not only measure the small number but also use anti-neutrinos to start to look for the difference between matter and anti-matter.

With just 2% of data the experiment hopes to take in its lifetime, T2K has shown that it has started a path down an exciting route. Efforts are now underway to get T2K up and running once more after the earthquake, so that we may continue this journey toward understanding the difference between matter and anti-matter and the creation of our Universe.

P.s. As a follow up I am writing a series of posts describing how we quantify the bizarre nature of the neutrino - check it out here.

First T2K Paper

2011-06-08T11:04:00.003+01:00

*** You can find the latest results here ***

Today the Tokai to Kamioka (T2K) experiment released its first collaboration paper. A technical paper, it describes the setup of the experiment and covers the entire infrastructure - how the experiment gets from neutrinos to data. The paper was immediately accepted for publication in the journal Nuclear Instruments and Methods A (NIM-A) and will be in next months edition of the journal.

All particle physics experiments begin their collaborative publications with a NIM paper before physics results are released. The description of experimental procedure in such papers are important to reference to make sense of any future physics results that are published. This is a massive milestone for T2K, which is the largest collaboration/experiment of its type with around 500 scientists and engineers working on the Japanese led experiment - see front page on which I have shamelessly highlighted my name :-) .

With the release of the NIM paper exciting times lie ahead for the T2K experiment as we anticipate physics publications. Watch this space.

You can get the paper from the pre-print arXiv here.
Please browse my blog for more info on the T2K experiment [1 2] , the detectors [3 4] used and physics behind the experiment [ 5 2 6 ]. Or leave me questions in the comments section and I will reply with a comment or a blog post if I have far too much to talk about.

Hunting Neutrinos at Super Kamiokande

2011-05-12T14:02:00.000+01:00

The Super Kamiokande (Super-K) detector is an amazing piece of technology. A 40m high and 40m diameter cylinder, it contains a huge amount of ultra pure with over 11,000 electronic eyes looking for feint signals of light. The light comes from charged particles travelling faster than light within water (for more on how this light is produced see my post Faster Than Light or and/or Slow Light).

The Display

The light from these charged particles is naturally projected in circular patterns on the wall of the detector, where the electronic eyes turn the light into an electric signal. This electric signal is fed into computers and a display of the light, which can be seen below, is constructed.

Each coloured dot on the display represents one of the 1000's of electronic eyes which has seen some light. The colour of each dot represents how much light the electronic eye has seen; purple being the least and red the most, the colours follow that of the rainbow.

The large unrolled cylinder is the main inner detector which has over 11,000 electronic eyes looking into ~33 Olympic sized swimming pools of ultra pure water. There is also a small volume of water entirely separated from the other with many less, just over 1000, electronic eyes. These eyes look outwards for charged particles coming into the detector from outside. The light seen in the outer detector is displayed in the unrolled cylinder on the top right of the display below.

 

Spotting a Neutrino

If you see an appreciable amount of light in the outer detector then any light seen in the inner detector is from a charged particle entering the detector from outside. This is the most common display you will see. Some Muons produced in cosmic ray interactions have enough energy to punch their way through the ~1km of mountain above Super-K and enter the detector. There are about 2 of these Muons entering Super-K every second.

If however you see no charged particle entering but view one in the inner detector then you have yourself a Neutrino interaction. Neutrinos have no charge but when they interact the produce charged particles such as the Electron and it's heavier cousin the Muon. So the characteristic of a Neutrino would be very little to no light in the outer detector but a visible charged particle in the inner detector.

Classifying a Neutrino

You will have seen by now that the patterns the light makes on the wall of the detector are circular. This is because the light produced by the particles comes out in a cone. If you keep watching you should see an event that leaves a ring pattern. This is a particle that has slowed to less than the speed of light in water whilst in the inner detector, after losing energy. You will also see many circles and these are particles that have not slowed to less than the speed of light before they exited the inner detector.

Sharp edged Muon rings and fuzzy edged Electron rings in the inner detector.

As I mentioned above the majority of events are cosmic ray produced Muons. Muons punch their way through the water as they are heavy weights, they leave a crisp edged ring/circle of light. Electrons are much lighter and as a consequence get jostled around. This jostling produces a fuzzier edged ring/circle of light. Using some sophisticated maths and example events we have an algorithm that can distinguish between these sharp Muon rings/circles and Electron rings/circles. Muons can only be produced by Muon Neutrinos and Electrons only by Electron Neutrinos.

You are now ready to go Neutrino hunting at Super-K so give it a go!

Can you spot a Neutrino? You would have to be very lucky! There are just a handful a day.
Can you spot an Electron Neutrino? Luckier still as there are far more Muon Neutrinos showing down.

Neutrino Bullets

2011-03-23T16:33:00.001Z

Firing 'bullets' of neutrinos allows the T2K (Tokai to Kamioka) experiment to know that the neutrino particles they see are the ones they are firing. I constantly talk about how T2K are firing neutrinos 295 km across (technically through) Japan. But I how do we know the neutrinos we see in our detectors are the ones we are firing? The short answer is that we are not firing a continuos stream, but instead intense 'bullets' of neutrinos and we use the timing of these bullets to know they are ours. For the longer answer read on.

Neutrino 'bullets' are fired 295km through Japan, from East to West.

A mean looking bunch of neutrinos!

As I described in my post "Birth, Death and Neutrino Beams" the neutrinos are created from the decay of other particles produced when crashing protons into a target. These protons do not come in a continuos stream, they arrive at the target in tight knit bunches. This close grouping means that the protons all hit the target within a few nanoseconds of each other (nanosecond is a billionth of a second). The newly created particles from this collision, Pion particles, are consequently themselves quite tightly grouped in the original direction of the protons. Eventually the Pions die (decay) and give birth to neutrinos.

The neutrinos created are not as tightly bunched as the Pions who subsequently are not as tightly bunched as the original protons. This spreading turns a grouping in time of a few nanoseconds to a few tens of nanoseconds. But this is still a very short period of time! Hence I chose to say that we fire neutrino bullets, in fact there are trillions of neutrinos in each 'bullet'.

We fire the neutrino bullets in semi-automatic mode with rounds of 8 bullets fired in short succession (a few 100 nanoseconds apart) and a small break in between of a few milliseconds. The pattern of semi-automatic fire is sent to the particle detectors as GPS time-stamps so they know when to brace for impact.

The neutrino are seen by detectors at 280m and 295km away from the smoking gun. GPS timing
tells them when to brace for the impact of a neutrino bullet.

The probability of the detectors seeing other particles in such a short time period is extremely small, so small as to be practically zero. Neutrinos are extremely few and far between due to their ghostly nature, only a handful of natural neutrinos are seen each day. Particles raining down upon the detectors from above are far more common but still the chance that one of these cosmic rays will coincide with a neutrino bullet is practically zero. In addition there are other ways we can discriminate between neutrinos and cosmic rays - like looking outwards to see if a cosmic ray coming in.

So we know the neutrinos we see are the ones we sent because of timing and the fact that the chance they are anything but the ones we sent is practically zero.

First T2K Results Announced

2011-03-16T16:49:00.005Z

*** You can find the latest results here ***

Today at 4pm GMT / 5pm EST Prof Andre Rubbia presented the first results from the T2K (Tokai to Kamioka) neutrino experiment at the NeuTel conference in Venice, Italy. The presentation of the results were delayed due to Friday's earthquake in Japan where the results were to be presented at seminars that afternoon.

Snapshot from a slide describing the T2K experiment.

The talk began with a statement from the spokesperson of the experiment Prof Takashi Kobayashi who was originally due to give Friday's seminar and the talk at NuTel. The statement read:

"Japan experienced very severe earthquake on March 11th 2011 at 14:46 JST. J-PARC facility suffered damages for some extent. There are no reports of casualties and all staff, graduate students, and foreign visitors have been located and as of evening Sunday March 13th all T2K members have been evacuated from Tokai area.

Fortunately enough, the Tsunami tidal wave did not hit J-PARC. We will start the investigation of the facilities. We will update the announcement as we learn the detail of the entire damage.

Our present priority is to restore life-supporting infrastructure such as electricity, water supply and gas at J-PARC. It may take some time, but we promise the full recovery of the J-PARC accelerator and T2K experiment in the near future.

I thank you for the messages of solidarity and sympathy.

Director of the Institute of Particle and Nuclear Studies, KEK

Koichiro Nishikawa

Spokesperson of the T2K experiment

Takashi Kobayashi"

The results presented are consistent so far with all previous oscillation experiments of this kind and there is no evidence as yet of muon to electron neutrino appearance yet. The analysis was done on a small initial set of data, updated analyses will follow in the near future with around 4.5 time the data/statistics. Once all data is analysed the new results should surpass the measurement accuracy of previous experiments in the field.

If you would like to see the presentational slides then please click here.

Any questions you may have please leave them in the comments and I will answer them.

First Results Postponed

2011-03-15T11:45:00.000Z

Road in Tokai-mura near the J-PARC facility.
Photo courtesy of Phil Litchfield.

The Tokai to Kamioka experiment, T2K for short, uses the science facility J-PARC located on the very East coast of Japan to produce a beam of particles called neutrinos. The first results from the experiment were to be presented at a seminar last Friday moments after the massive 9.0 earthquake hit north eastern Japan. The damage to the facilities used by the experiment and the devastation left in the wake of the disaster have meant that the first results are now to be presented tomorrow at 5pm at the 14th NuTel International Workshop on Neutrino Telescopes in Venice, Italy.

The experiments spokesperson Professor Takashi Kobayashi was due to present the results at the seminar and at the Venice conference but has chosen to remain in Japan to assist in the clean up effort. First results will instead be presented by another senior member of the T2K experiment, Professor Andre Rubbia. Watch this space for more on the first results.

Big Bang Fair

2011-03-14T22:27:00.000Z

Last week I was lucky enough to take part in one of the biggest expositions of science and technology in the UK - The Big Bang Fair. Hosted at ExCel in London's docklands the events saw over 20,000 young people from all over the UK come to learn about science, technology and what it is like to have a career in the sector.

In many talks I have given and chats that I have had in pubs the phrase "building blocks of nature" gets used every time to describe particles. It therefore seemed a natural progression to use building blocks to explain particle physics. Armed with 22,000 LEGO block and 1000's of instruction manuals we went through a whistle stop ride through the history of the Universe and the forces of Nature.

Me on the stand building protons with students.

I feel it was all a rather massive success with all ages. Primary school children seemed to accept that the Universe is built from basic blocks at the smallest level and that it is the forces, like gravity, that give instructions to clip the blocks together. Secondary school children got to learn that protons and neutrons are made from small building blocks called quarks and that the strong an weak nuclear force are responsible for how the assemble themselves into heavy elements.

The Big bang was a VIP rich event the most important VIP I spoke to was Dame Professor Jocelyn Bell who, as almost everyone who came to our stand, loved the idea; although Professor Bell didn't want to make a proton.

If you are a teacher or would like to know more about the workshop please contact the outreach team at Queen Mary, University of London.

Earthquake

2011-03-14T11:42:00.002Z

On Friday 11th March an Earthquake of magnitude 9.0 on the Richter scale hit the North-East of Japan and Tsunami waves shortly followed. The effects of the quake were felt through large swathes of Eastern Japan. The small town of Tokai-mura in Japan is home to one of the most advanced and important scientific facility in the world; the Japan Particle Accelerator Research Centre (J-PARC). The J-PARC site hugs the coastline and is home to a chain of particle accelerators and a nuclear power plant which service numerous biological, materials and physics experiments.

The experiment of which I am a part, Tokai to Kamioka (T2K), was to announce latest results at a seminar before the events of Friday took place. At J-PARC T2K produce a beam of neutrino particles and measure their bulk properties before they embark on a 295 km journey to the West of Japan. Today experts are on site investigating the extent of damage caused by Fridays events.

A road on the J-PARC complex subsides after Fridays earthquake.

I am pleased to have heard over the weekend that all of my colleagues who were living and working in Japan are safe. All foreign nationals are being repatriated, travelling home within the next week. My thoughts go out to those who were not so lucky.

Slow Light

2011-01-27T15:32:00.000Z

The natural speed limit of the Universe is the speed of light, that is the speed light travels when it is unhindered such as in the vacuum of deep space (air is a good approximation of this). When light travels through matter however it slows down and the reason for this is the dense collection of electrons.

Electrons are negatively electrically charged and tell the world so by constantly emitting electromagnetic information. This information exchanged by the photon, the electromagnetic force carrying particle. The photons are virtual, which means they do not actually exist. Energy is borrowed from the Universe/particle to create them and it is given back when the messenger delivers it's message. This is the electromagnetic field, the same thing we can see in action with iron fillings around a bar magnet.

A Feynman diagram of an electron telling another electron it exists. A virtual photons exist in space but not time.

When a photon travels through matter where there is a high concentration of electrons, and therefore a large electromagnetic field, then it gets dragged back. We say it gets 'coherently scattered forward' which is kind of like getting absorbed and re-emitted when it is constantly interacting with the electromagnetic field. It is like trying to run normally (light in air/vacuum) and then through treacle (light in glass/water) - you (light) are slower in the treacle (glass/water) because you are interacting more with your environment, the friction (electromagnetic field) is stronger.

In this way it is not against the speed limit of the Universe for a charged electron or muon to have enough energy to travel faster than light can in water or glass - this is what is happening in Super Kamiokande and other detectors like it.

In the same way that air cannot get out of the way of a jet fighter quick enough the virtual photons cannot get out of the way of the charged electron or muon quick enough. This results in a build up of tension, from a bunching of the electromagnetic field (seen in the figure below). This tension is released in stealing energy from the charged particle (and therefore slowing it sown) to make virtual photons into real photons - light. This effect is known as Cherenkov radiation, after the Russian physicist who explained it.

*This was a very quick blog post! There may be mistakes.*

The Death of a Giant

2011-01-06T11:20:00.000Z

In my previous post I talked of the field of neutrino astronomy and how we can use neutrino particle detectors to construct a picture of a the Sun. Perhaps the most famous piece of neutrino astronomy is however the observation of neutrinos from the explosive supernova death of a star. The light from the death of such a star reached us on Earth from over 168,000 light years away on February 23rd 1987 and so too did a much larger amount of neutrinos.

After and before shot of the star which came to be know as supernova
1987a, the arrow points to the star before the explosive death.
Picture courtesy of the Australian Astronomical Observatory/David Malin

The supernova was bright and easily visible with the naked eye in the night sky, as the after (left panel) and before (right panel) picture to the left shows. This huge amount of light is less than 1% of the energy released when a giant star dies through a supernova. A whopping 99% of the energy is released in (anti)neutrinos!

Just one or two (anti)neutrinos per day out of the trillions upon trillions raining down each second were seen in the Kamiokande II detector (the predecessor of Super Kamiokande). But on the 23rd February 1987in the space of just 13 seconds the Kamiokande II detector saw eleven!

The (anti)neutrinos were also seen by other particles detectors; IMB in the USA saw 8 and Baksan in Russia (the then USSR) saw 5 within the same short time period. This was unprecedented! If it takes a whole day of trillions upon trillions raining down each second just to see one or two think of the huge number of neutrinos that bathed the Earth in those few seconds.

With these results the field of neutrino astronomy was firmly founded. Now the wait is on for the next near by supernova hopefully this time within our own galaxy, the Milky Way, so that we may learn more about the impressive demise of a once great star.

More Than One Way to Look at a Star

2011-01-05T11:37:00.004Z

After watching BBC's stargazing last night I want to remind people of another way to 'look' at a star. Instead of using photons, particles of light (*) one could use other particles spat out a star. Particles with electric charge, such as protons and electrons, are easily manipulated by magnetic fields (brilliantly described by Dr Lucie). So any picture we want to get of a star with charged particles will be modified by the magnetic field, which is brilliant if the magnetic field is what you want to measure.

The Sun as seen in neutrinos, from 1 km underneath a mountain in
western Japan. Picture courtesy of ICRR University of Tokyo.

Neutrino particles on the other hand have no charge at all and fly straight and true through the cosmos from their birth within a star. A brilliant picture which I find amazing is one of the Sun by the Super Kamiokande detector. Super Kamiokande is in the heart of a mountain underneath 1km of rock so the only way it can see it is through neutrinos.

These neutrinos are being produced in their trillions every second in the same fusion reactions which produce the light we see from the Sun. It may take the photon light particles 1000's of years to exit the Sun (around 100,000 years for those in the very centre) as they get jostled by all of the charged particles. Neutrinos on the other hand are not bothered by electric charge and rarely interact with anything around them. They fly straight and true directly from their place of birth in the Sun and some reach the Earth in around 8 minutes (about 66 billion times faster from the centre!).

A handful of these trillions upon trillions of neutrinos which reach the Earth are seen interacting in the 33 Olympic sized swimming pools of ultra pure water in Super Kamiokande, and it is from these few a picture of the Sun can be constructed. This is just one example of neutrino astronomy, rather than standard electromagnetic astronomy.

So next time you look at the Sun remember that you are looking a very old light but there are trillions upon trillions of very young neutrinos passing through your body on their long journey our into the cosmos.

(*) Not only particles of light but all electromagnetic radiation from radio to X-Ray and beyond, they are just photons of different energy.
(+) Photons are the carriers of the electromagnetic force and so interact readily with electrically charged particles.

Birth, Death and Neutrino Beams.

2011-01-04T14:40:00.004Z

In the T2K (Tokai2Kamioka) experiment we begin our science in a chain of death and birth. T2K uses the worlds most powerful beam of neutrino particles to understand more about the creation of our Universe. A neutrino beam sounds like something a Bond villain might use to hold the planet to ransom; But as I mentioned these ghostly particles are not threatening in any way (despite what the writers of the film 2012 say!).

Showers of particles from cosmic protons.

Beams created with conventional particles, such as protons, make use of the fact that they have electric charge and can therefore be accelerated by electric fields as well as pinched and manipulated by magnets into a fine stream. But neutrinos have no charge, so how do you create a beam of them? As with many other technologies we copy Nature.

Protons are constantly being accelerated by the Sun and many other cosmic sources, some of them rain down upon the Earths atmosphere. When a proton strikes the atmosphere it gives birth to a shower of new particles; its energy is turned into mass using Einstein's E=mc2. The majority of the newly born particles are a type called pions.

The death cycle of a pion.

Pions are short lived, they die quickly and give birth to yet more particles which rain down upon us from all directions, created all over the Earths atmosphere. Some of these new particles may also die and give birth to yet another generation of brand new particles.

The picture to the left was taken with a particle detector called a bubble chamber (*), it shows the death cycle of a positively charged pion (blue). In death the pion gives birth to an antimuon (green) and muon neutrino before the muon then dies, giving birth to a positron (red) and electron neutrino. The neutrinos cannot be seen here as only particles with electric charge can be seen (the coloured lines are drawn on the picture to guide the eye).

In the T2K experiment we copy this process. We accelerate our very own protons, just like the Large Hadron Collider at CERN, and smash them into our own target. We don't have a jar of atmosphere to smash our protons into but instead use graphite; the same stuff you'll find in the centre of your pencil.

Horns to focus pions into a beam.

To create a beam we don't want the neutrinos to go in just any direction, so we need to focus them. With no charge we cannot effect the neutrinos directly, but the pions do have charge and in their short lifetime we focus these into a beam.

Surrounding our graphite target and beyond there are a series of three metal horns which look a little like the exhaust of rockets. For short nano-second (a few billionths of a second) periods a huge amount of electricity is pumped through these horns (~300,000Amps! About 100,000 times that of a standard household plug!) to produce a magnetic field which focuses the pions into a beam. Because the pions are travelling at such high (relativistic) speeds the neutrinos and muons, created when they die, carry on in the same direction. So in creating a beam of pions we in turn create a beam of neutrinos and muons too.

Smashing Stuff: From accelerated protons to neutrino beam and the first
set of particle detectors at J-PARC in Tokai-mura, Japan.

The beam of pions transform into muons and neutrinos as they travel through a 110m tunnel filled with Helium. At the end of the tunnel there is a massive block of concrete and metal which absorbs the muons and remaining pions. The neutrinos continue their journey unfazed, firstly 280m to a collection of particle detectors and then on through the Earths crust to the Super Kamiokande detector 295km to the West.

The route of the neutrino beam from creation at the J-PARC proton accelerator to Super Kamiokande 295km away.

(*) Bubble chamber detector: Superheated liquid, heated well above it natural boiling point, is held in a pressurised container to prevent boiling. As a particle with electric charge passes through the liquid it deposits energy, in the form of ionisation where electrons are stripped from their atoms. This extra energy allows small bubbles of gas, boiling, to occur along the path of the particle, which is what can be seen in the photograph.

Masochism

2010-12-02T10:38:00.000Z

On Saturday I have a 12 1/2 hour flight to Tokyo followed by a 2 1/2 hour bus ride to the sleepy little town of Tokai-mura in Ibaraki prefecture on the East coast. I never sleep on planes so it will be another 36+ hour day until I finally sleep. I'll then wake up at 4am after 6 hours sleep and begin a frantic week of meetings which will be more 12 hour days than not, sat in a conference room that could be anywhere in the world. It will be the fourth time this year I have done this. Why would I do this to myself?

The simple answer is because I enjoy it, twisted I know. The meetings themselves, though stressful, are brilliant. You get a front row seat to watch the story of one of the biggest experiments in the world unfold before you; organising, planning, problem solving and most importantly doing science. I also enjoy the socialising with my colleagues from around the globe; The lunches and dinners of tasty Japanese food. The final day collaboration party is always worth waiting for too, usually ending up with authentic Japanese Karaoke.

I have started blogging with some ferocity over the last month and have maybe been writing a little too quickly at times. Over the next few weeks I will bring the pace down a little and write a series of four posts on the T2K (Tokai to Kamoka) neutrino oscillation experiment. I will start with how we create a neutrino beam in the coming days and continue the neutrinos journey from creation to possible final detection.

After this series of posts I want to know what you want to know about! I love just rambling on about my field of research but I always enjoy questions more. So if you have any questions about particle physics or the early Universe then mail, tweet or leave comments here on my blog. In the new year I will then work my way through and answer them.

Four Neutrinos? But You Just Said There Were Three!

2010-11-30T10:33:00.001Z

3 Neutrinos, 2 mass differences.

My last post talked about the undeniable evidence which states that there are three generations of particle, identical in every way but one, they get heavier and heavier in mass. Results from neutrino experiments have hinted though that there might be a fourth. But how?

From measuring the identity crisis of the neutrino we can determine the difference in mass between the different neutrinos. We can know the difference in mass of the three neutrinos with just two numbers; the size of the mass difference between neutrino 1 and 2 and the size of the difference between neutrino 2 and 3. The difference between 1 and 3 can be calculated from these two. This is the same as only needing to know the length of two cross pieces between three irregularly spaced fence posts to know the size of a fence.

Experiments looking at the indecisive nature of the neutrino have measured the two differences by looking at how often electron neutrinos (12 difference) and muon neutrinos (23 difference) change their minds over 100's of kilometres. Then along came the LSND experiment. LSND, which stamnds for Liquid Scintillator Neutrino Detector (of course!), used muon type antineutrinos and claimed to see them change into electron type antineutrinos over a short distance of just 30 metres. This did not fit in with the other two mass differences seen. This mass difference was at least 1000 times bigger than the two measured previously.

Extending the fence about 1000 times the original length and adding a new fourth neutrino fence post.

The simplest way to be able to explain this change over such a short distance would be to include another mass difference. With the two differences explaining the three neutrinos, a third mass difference would require an extra fourth neutrino.

But in my last post I said that there could only be three neutrinos. Three neutrinos and only three neutrinos (and other generations of particle) can interact via the weak force as explained in the standard model maths. There is nothing to say that other neutrinos, which do not interact via any forces, could exist. These neutrinos would be called sterile, as the do not interact via any known force (except gravity, but as I mentioned we ignore that when talking particles). But this would be a huge overhaul in our picture of our Universe.

Lots of people like the idea of these sterile neutrinos; they would be a great candidate for Dark Matter; 25% of the Universes energy which we cannot explain. But one experiment iss not proof. You needed to be able to repeat the results and say with great confidence that what you are seeing is a real effect. To this end other experiments were devised to test the LSND claim.

The MiniBooNE Detector
Image from FNAL

In September last year the Miniboone experiment, which was devised to confirm or refute the results of the LSND experiment, published inconclusive results. Not enough photographs of neutrinos taken. Just a few weeks ago, however, they published a new paper with 1.7 times more photos, and the results were very interesting indeed.

Miniboone used both neutrinos and antineutrinos in their experiment. When firing neutrinos they saw no evidence that muon type were deciding to become electron type neutrinos. When firing antineutrinos they saw a different story. When firing muon antineutrinos there was an excess of electron type antineutrinos seen in the detector. This result fits in with what the LSND experiment saw.

Now the race is on to explain these results. Is it a fourth generation of sterile neutrino? If so these results tell us that it would also have to violate the the symmetry between matter and antimatter, as it is seen predominantly with antineutrinos. It might just be an unknown effect or misunderstood interaction of the neutrino, which is still an enigma of a particle in many respects. Miniboone will continue to take photographs of neutrinos with their detector and hope to present new results soon with yet twice the number again. Meanwhile theorists will continue to concoct lots of different ideas about sterile neutrinos and ways to explain the data.

It is much more exciting to see something we did not predict or expect, even better to see it time and time again. Science is all about explaining the new and pushing the boundaries of knowledge. Whether it turns out that there are sterile neutrinos around us or it is just an as yet unexplained effect, it is just another reason why 2011 is going to be an exciting year in particle physics.

Why Only Three Generations?

2010-11-23T13:01:00.000Z

The Standard Model, Forces and Particles

In my Particles post I mentioned that there were twelve building blocks of Nature, four which make up most of the stuff around us and then two more sets of heavier cousins; exactly the same in every way just heavier. These increasingly heavy groups of four we call the three generations of particle. But why only three? Why not four, five or just the one? We don't know. Nature decides these things not us. We have, however, measured to high accuracy that there are just three of these sets which play out the story of Creation, using the forces we experience in our Universe.

As I talked about in my last post, all forces are exchanged between these building blocks by specialised particles called bosons. The way in which these special bosons interact with the twelve building block particles is described successfully in a collection of maths we call the Standard Model.

I want to focus on one of these boson particles, the Z. As previously mentioned the Z boson is essentially a photon that weighs something; where the photon (particle of light) is entirely mass-less, the Z weighs in at almost 180,000 times the mass of an electron! The heavy Z only lives for a fraction of a second and from the death of this heavy photon that we can determine how many generations of certain particles there are.

Death of a Z

The Standard Model maths tell us how the Z boson will die and how often it will die in a certain manner. The energy of the Z goes into creating matter using Einstein's famous equation E=Mc2, and is seen to always form equal amounts of matter and anti matter; usually in pairs of one matter and one anti-matter particle. As a carrier of the weak force, which can be felt by all of the twelve building blocks, the Z can give birth to pairs of particle and antiparticle of any type.

Before the Large Hadron Collider (LHC) was built the Large Electron Positron Collider (LEP) occupied the same tunnel at CERN in Geneva, Switzerland. Instead of accelerating protons it accelerated electrons and their anti-matter version the positron. LEP was designed, amongst other things, as a factory to produces 1000's and 1000's of Z and W weak force carriers to measure their properties accurately - which is exactly what they did.

The detectors of the LEP experiment photographed the death of many Z bosons, watching them turn into quark-antiquark(*), electron-positron, muon-anti-muon and tau-antitau pairs. From these pictures physicists could determine the strength of the electroweak forces at play. The rate at which the different types of death of the Z were seen allowed predictions to be made about how often they should see other types of death. So from counting the number of times a Z would give birth to an electron and positron you could predict, using the standard model maths, how often you would expect to see it give birth to pairs quark-antiquark or tau-antitau(+).

One of the very first pictures of particles seen in the Aleph detector at LEP.

Some of the time the Z boson seemed to vanish into thin air. No quarks. No other charged particle to be seen. Here neutrinos and anti-neutrinos were being born, flying straight out of the LEP detectors unseen. The rate the Z would give birth to each neutrino type could be predicted using the standard model maths and information from the other types of Z death (plus other independent sources), but because the neutrinos were invisible it could not be determined directly whether they were electron, muon or tau type neutrinos and antineutrinos. All that could be determined was the total number of times the Z vanished into thin air by giving birth to neutrinos.

Standard model maths tells us the rate at which the Z turned into electron, muon or tau type neutrino-antineutrino pairs is equal. In 1990 the Aleph detector, part of the LEP experiment, announced that the total 'missing energy' deaths was equal to three times this probability (+). This was evidence, 98% confident, that there were not four but only three generations (types) of neutrino that interacted via the weak force. If there were more then the rate at which Z died to form neutrinos would be greater.

It follows from the symmetries used in the maths of the standard model that there are only three generations of the other particles too. So Nature has chosen just three generations of particle. Certainly only three which fit in with our current picture of the Universe.

There has been talk recently about the possible discovery of a fourth generation of neutrino. More about this some next time.

*Quarks are never seen alone, they instead for jets of particles, from these jets one can determine what type of quark was born.

+Link to the paper.

May The Electroweak Force Be With You...

2010-11-22T12:47:00.000Z

So I have talked about the building blocks but what about how they interact with one another? These are the forces. There are three we care about in the ultra small realm of the particles: the electromagnetic, weak nuclear and strong nuclear force (gravity is far too weak to be noticed, so we don't bother with it here).

Skaters exchanging a force.

Forces are exchanged by special particles called bosons, thrown between the twelve fundamental particles as messengers. The messages they carry tell the particles how to react, such as where to move or how to change. A good analogy of this exchange of messenger boson particles is as follows: Two skaters stand still on an ice rink facing each other, one throws a ball to the other and they start to move apart. They continue to throw the ball and move further apart. This demonstrates two same electrically charged particles (the skaters) forcing each other apart by exchanging photons (balls), the carrier of the electromagnetic force. With some forces however the message may tell the skaters that they need to get closer or even change what they are entirely.

The message of the electromagnetic (EM) force is passed between particles by the photon. Photons are particles of light. The properties of the EM force and the fact that photons have no mass what-so-ever mean that the influence of the EM force can be felt beyond the nucleus and the atom - this is why you can power the computer/phone you are reading this on.

The weak nuclear force is carried by not one, but three different boson particles. Two of these particles, W+ and W-, also have electronic charge and so themselves feel the EM force. In fact the EM and weak forces have been found to be one and the same force which is called electro-weak (more about this some other time). The W+/- are responsible for particles changing, as seen in nuclear decays or the forming of heavy elements (fusion) in the Sun. The third weak messenger is the Z. The Z boson is essentially a photon that weighs something; where as the photon (particle of light) is entirely mass-less, the Z weighs in at almost 180,000 times the mass of an electron!

W+/- bosons also have mass and weigh in slightly lighter than the Z at about 161,000 times the mass of the electron. The fact that these three weak force carriers have a mass means that they cannot live for long/travel very far. The Universe wants nothing more than to be at the lowest energy it possible, lazy git! This is why an apple falls to the ground and not out into space, why electrons will not move around wires by themselves and why nothing will change unless some one/thing exerts effort.

So heavy particles and constantly wanting to lose weight and they do this by changing into something entirely different. The Muon changes into the electron and the weak force messengers change into a wide array of things. The heavier something is, the less stable it is and the quicker it wants to lose weight by changing into something new. These very heavy Z and W+/- cannot even get out of a nucleus before changing, this is why we say the weak nuclear force as it is restricted to the nucleus.

The strong force is a whole other kettle of fish and this post has already become long so I will discuss this a different time.

Brangelina and the Top Quark: A Higgs Tale

2010-11-18T11:59:00.000Z

Z-list Neutrino 'Celebrities'

I was asked by a friend to explain how the Higgs gives mass to particles with an everyday analogy, he liked it so I thought I'd share. Here was my response.

Imagine you have been lucky enough to attend a red carpet premiere of the latest Hollywood block buster. Surrounding the carpet are hundreds of paparazzi waiting to get that perfect photo. You and me would be of no interest to these guys, who would by a photo of me? And so we can get out of our car and walk the length of the carpet as fast as we like and take our seat in the Cinema.

Next imagine a Z-list celebrity, like the latest recruits from "I'm a Celebrity, I'm a Celebrity ... Honest I am". The paparazzi will show a little interest and they may be shouted at to pose for a couple of photos. This will slow our Z-lister down a little meaning that they can't go and sit down as quickly as the pleb that is me.

A-List Heavy Quark Couple Brad and Angelina

Suddenly the A-listers start arriving and the paparazzi go crazy, every single one of them shouting out to get Brad and Angelina looking into their camera. This makes the walk on the carpet from Limo to Cinema a long one, constantly posing for photos to satisfy the paparazzi.

The paparazzi are Higgs Bosons. The people walking the carpet, from A-Z list celebrities and common folk, are one of the fundamental particles, Natures basic building blocks. The interaction between the paparazzi (Higgs) and the people on the carpet (particles) is to do with how famous (massive) they are, the more famous (massive) the more they want a photo and the slower the person (particle) moves.

Unhindered all particles would travel at the speed of light in empty space, because this is the natural speed of the Universe. In the way that you or me walking down the red carpet would not get the interest of any paparazzi, particles with out mass, such as particles of light (photons), travel at their natural top speed.

Celebrities are the same as particles that have mass, cannot reach their natural top speed (unless they have access to infinite energy) because they are slowed by pointing cameras. The more famous (massive) the slower the celebrity (particle) can move.

The comparative masses of the fundamental particles.

In this way the Brangelina 'particle' is like the Top Quark, the heaviest of the Universes LEGO set. Z-listers like the latest motley crew on "I'm a Celebrity" would be nothing but Neutrinos, the lightest of the fundamental particles (and thought for a long time to have no mass/fame!).

You can see from the picture that the top quark is so much more heavy than the other particles. Who would make up your celebrity standard model? Which super star would be your top quark? What about the neutrinos with their tiny masses/fame?

Symmetries and the Birth of The Universe

2010-11-15T12:56:00.001Z

And Then There Was Light, Matter and Anti-Matter

Nothing. No planets or stars. No space or time. No light or dark. Nothing. That is until an unimaginable amount of energy unfurls from a single point. Space and time are born. The energy carried by particles of light, photons, as fast as they could travel.

As Einstein wrote in his most famous equation E=mc2 :from energy, E, you can create mass, m. Particle physicists such as myself use this principle to create a menagerie of things in the smallest realm of nature. When we perform our experiments we create matter, the stuff in the atoms that make the planets, stars and entire visible Universe in which we live. We also create equal amounts of something called anti-matter.

Anti-matter is a mirrored reflection of the constituents of atoms, exactly their opposite in every way, except they have the same mass. If one were upwards the other would be downwards, one hot then the other cold. In the same way a movement up can cancel down and heat can eliminate the cold, matter cancels anti-matter. When the two meet they cease to exist and form pure energy, which is usually light. So the light which gave birth to the matter and anti-matter lives once more.

According to current experiments this cycle of destruction and creation would continue, until all of the light

had so little energy that it could not produce the lightest mass matter and antimatter anymore. This would leave the Universe today as a collection of nothing but microwaves - similar to the picture of the microwave universe take by the WMAP satellite (left). No atoms could form, no stars would burn and no planets would exist to nurture fragile complex life. A good analogy would be heating a room and cooling with equal power simultaneously. There would be warm and cold patches dotted around but after some time the net effect would be zero, the room would be exactly the same temperature as before.

So how are we here?

Raw material for all we observe, and continue to discover, was created in the first few seconds shortly after the Big Bang of energy. The fuel for stars, the very first matter, had to have been created in larger amounts than the mirror counterpart anti-matter. With the trillions and trillions of times that the energy-mass-energy cycle was spinning every fraction of a second, it only needed to be a rare occurrence that more matter was produced.

Over production of matter came in collisions between the smallest possible building blocks, the elementary particles. Bit by bit rare extra matter creating interactions produced the fuel for the first stars which then proceeded to create the Universe today. Without those rare interactions nothing would exist.

To understand these rare interactions is to determine the origin of the material Universe as we see it. To see something as rare as the extra matter creating interactions scientists study billions upon billions of interactions.

This bias towards matter can be explained in the language of science, mathematics, with a slight imbalance in the symmetry between matter and anti-matter. A symmetry occurs where we can manipulate something and return to the same picture we started with; for example if we rotate a square 90 degrees in either direction we get back to the same square, this we call rotational symmetry. Just the same we can reflect a picture of a square in a mirror and the reflected square looks identical to the original, this is reflectional symmetry. We use manipulations such as reflection and rotation in our mathematics to do this with our picture of the Universe.

Let us take a simplified picture of the Universe in the form of a wood cut tessellation of flying fish by the artist MC Escher (below). This is essentially our picture of the Universe as we measure it in our experiments each day, equal amounts of matter (white fish) and anti-matter (black fish). What we will now do is manipulate this picture and hopefully get back to exactly the same, to find a symmetry. We do this from left to right in the picture below.

Tessellation by M.C. Escher, modified by me idea © Ben Still

First we take a negative of the picture, turning all that is black to white and visa versa. The picture now looks nothing like the original so lets think of other manipulations we can perform. Lets turn the picture over, rotating it so that everything on the left is now on the right and right on the left. OK, still not back to the original. I remember the black fish in the middle pointing upward so lets flip the picture again, this time everything on the bottom to the top and top to bottom.

There we have it. The same picture we started with... well almost. You have probably noticed a small difference in the eyes of the fish. This is an exaggerated version of what occurs in our Universe between matter and antimatter. This small difference, or asymmetry as we call it, is present in Nature but at a much smaller level than is shown here by the eyes of the fish. In fact if we were to represent the amount thought to be present in Nature then it would effect about one pixel in this picture - the worst spot the difference puzzle ever! But it is exactly this difference that we are searching for and in the T2K experiment we hope to do this using the most ghostly of natures building blocks, the neutrino.

The technical name for this asymmetry is CP violation, which stand for Charge-Parity violation. Charge is the first manipulation we performed by taking the negative of the picture, effectively turning all matter to anti-matter and visa versa. Parity is a fancy word for directions in space. So the two changes left to right and up to down are the parity changes. The symmetry between matter and anti-matter is therefore called CP symmetry and as I mention the difference, or asymmetry, is a violation of this.

This post is actually taken from the research page on my website, please visit for more physics and information about my research.

Identity Crisis In Japan

2010-11-10T15:05:00.000Z

The Confused Neutrino
Modified from Wikimedia Commons

When you get to the smallest realms of Nature the world becomes very strange indeed. Instead of certainty, there is probability; things only existing when 'seen' and at all other times they are but a cloud of possibilities. With neutrinos we can see the effects of this bizarre world on the macroscopic scale which we are familiar with day to day.

Because the neutrino is so small, ghostly and difficult to see it remains in the strange world I mentioned earlier, sheltered from all other things. With time as nothing but a cloud of possibility, it starts to have an identity crisis. Am I an Electron neutrino? Muon neutrino? Or perhaps a Tau neutrino? Born as one type the Neutrino starts to re-think what it wants to be and it becomes a mix of all three possible types Electron, Muon and Tau. These types are defined by what charged particle they are always found with.

It is not until we 'see' the neutrino interacting with stuff in our detector that we force it to make a choice. When interacting it gives up its life to give birth to one of the three charged particles, depending on what neutrino it chooses to be in its forced snap decision.

Time stands still when you travel as fast as
light. Picture from Wikimedia Commons

Neutrinos were first thought to not weigh anything, like photons (particles of light), and so would travel the natural speed of the Universe, c, the speed of light in empty space. At this speed the Neutrino could not have an identity crisis, at this speed time itself stands still; so there would be no time for the neutrino to think that it wanted to be something else. The neutrino could only have an identity crisis if it weighed something, or as we say has a mass.

In 1998 the Super Kamiokande experiment proved for the first time that neutrinos were deciding to change, from Muon to Tau type. This overturned the original picture we had of the Universe in which neutrinos had no mass. Super Kamiokande led the way to more precise experiments who have since then been trying to better understand the identity crisis of the neutrino.

The T2K (Tokai 2 Kamioka) experiment on which I work is the latest and greatest of these experiments. We are firing the worlds most intense beam of Muon neutrinos 295km from the very East coast of Japan (Tokai) to the Super Kamiokande detector (Kamioka) in the West. We learnt that Muon neutrinos decide to become Tau type but have never 'seen' them decide to be electron type. This is what we are looking for. In my next post I will talk about why we we want to see this and what it can tell us about the creation story of the Universe.

Firing a beam of neutrinos 295km from the J-PARC particle accelerator on the East coast of Japan to Super
Kamiokande in the West. © Ben Still

Electrons and Muons

2010-11-09T10:26:00.000Z

The Electron and the Muon
Picture from Wikipedia Commons

In the last post I started talking about the charged leptons and in particular the Electrons and Muons. As I said the only difference between these indivisible building block is that the Muon is just carrying a little more weight, in every other way they are identical. This extra weight is enough though for the Super K detector to distinguish between these two.

As I showed in my 'Faster Than Light' post these charged particles produce light when they travel faster than light in water. This light comes out in a cone an casts great circles and rings on the walls of the huge Super K detector.

Because the electron is fairly light it gets jostled and bumped about fairly easily in collisions with other Electrons flying around the atoms in the water. In these collisions the Electron can give up a large portion of it's energy to these other spectator electrons; so much so that they can then fly off at faster than light in water and in turn produce their own optical sonic boom (see Faster Than Light). This means that the circles and rings which Electrons produce in Super K get blurred and look a little fuzzy.

Arnie powers his way through.
From Kindergarten Cop.

The Muon on the other hand isn't bothered much by the tiny Electrons whizzing around the atoms in water. It punches its way straight through in a straight line. This produces much sharper, more focused circles or rings.

You can think of an Electron as a 5 year old running their way through a crowd of their classmates, getting bumped about and possibly bouncing off (imparting some energy to) one or two. Now imagine a fully grown Arnold Schwarzenegger running through the same crown of 5 year olds; no problem for him to power his way through undisturbed.

This isn't even near representing the weight difference between the Electron and Muon. Arnie is just over 6 times as heavy as an average 5 year old. The Muon on the other hand is whopping 200 times heavier than the Electron. This would be equivalent to a small Elephant pounding it's way through our group of 5 year olds!

What an 'typical' Electron looks like in Super K
By Tomasz Barszczak

What an 'typical' Muon looks like in Super K
By Tomasz Barszczak

Clever techniques recognise these different fuzzy and sharp ring patterns (like the ones shown above). These techniques allow us to say with quite a large amount of confidence that we have seen an Electron or Muon purely from the pattern of light produced. Above are plots of what 'typical' Electrons and Muons look like in Super K. Each grey or coloured dot is one of our inverse light bulb electronics. The colour represents the time that light was seen by these electronic eyes and the size of them represents the amount of light each sees.

Other clever techniques allow us to calculate the direction and energy of the particle. The direction can be reconstructed from the centre of the ring cast on the wall (the diamonds in the above plots). The energy comes from the amount of light seen, there is a direct relation between the two.

So once we know if we have an Electron or Muon, the direction it was going in and the energy it had we can tell what neutrino came into Super K and the source it came from to a high degree of accuracy.

Next - Identity Crisis in Japan

Particles

2010-11-05T14:32:00.000Z

Chopping up Nature to find out what it is made from.
Picture from Wikimedia Commons.

I have been talking about things called particles but haven't really explained them. Until now. If we took anything around us and started chopping it up into smaller and smaller and smaller bits we would eventually reach a point where we could no longer cut it in half. What would be left with are things called fundamental particles. They are natures LEGO set, the building blocks from which everything in our visible Universe surrounding us is constructed.

Nature has a very limited number of different pieces in this construction set, just twelve in fact; there are many more different types of block in most LEGO sets! It is these twelve which are used by nature in many different and creative ways to build the varied and wonderful array of things in the Universe around us. The twelve blocks are the ones in green and pink on the left of the picture below.

Natures LEGO set and carriers of the forces (no Star Wars pun intended)
Picture created by Me, © Ben Still

In this blog I am going to focus on the green blocks which are as a group are called leptons; in particular the three at the bottom, called Neutrinos.

I would not be surprised if you have never heard of Neutrinos but you may be surprised to know that they are the most common, most numerous of the twelve building blocks of nature. Right now there are around 50,000,000,000 passing through an area the size of your thumbnail every second.

You probably haven't heard of them because they are ghosts. With 50,000,000,000 going through just your thumbnail each second, think of the trillions going through your body each minute. Now think of the ridiculous large number that would have passed through your body in your lifetime. Even if you live to be the ripe old age of 100 you would be lucky if just one of these huge number of neutrino even noticed you existed.

So why is this? Well the solid feel of things around us is an illusion. Touch something around you and it 'feels' solid; your hand does not pass through, it is physically stopped. But this is not because something is actually there, over 99.99999% of the 'solid' stuff is in fact entirely empty space. The illusion that something is solid, or bigger than it actually is, comes from the forces; the ways in which these particles communicate and interact with one another.

The electromagnetic force at play. Hair stands up because
electrons have been transferred from one thing to another
giving things an equal and opposite charge which
produces an attractive force.
Photo from Wikimedia Commons

The force that make things feel 'solid' they way they do is the electromagnetic force; the same thing that makes you hair stand on end when you rub a balloon on it. It feels solid because the negatively electrically charged electrons whizzing around the atoms in the solid thing are pushing back against (repelling) the electrons whizzing around the atoms in your hand. The closer they get the stronger the force until it gets so strong that you can no longer move your hand against it.

The actual 'solid' stuff, the less than 0.000001% that is there is, can be found locked up almost entirely in the very centre of each atom making up the material, in a place called the nucleus. In the nucleus you find almost all of the mass of the atom in the form of things called protons and neutrons, which are made themselves from the pink blocks in the picture above (more about these another time).

A neutrino has no electric charge and therefore does not see stuff (atoms) to be as 'solid' as we do. The only force the neutrino feels is a force called the weak nuclear force. Weak because it is not as strong as the electromagnetic and nuclear because it can only be felt within distances smaller than the size of the nucleus. So to the neutrino 99.99999% of atoms, the stuff around us and us, is actually empty space. For the neutrino to have a chance of 'seeing' something it must hit this 0.000001% and even then there is only a slim chance, thanks to the weakness of the force, that the neutrino will actually do anything.

Stealthy Neutrino the Ninja.
Photo from Wikimedia Commons.

On the rare occasion a neutrino does choose to grace us with its presence then it gives up its life to create one of the three electrically charged leptons, the upper row of green blocks. The electron, which I mentioned are whizzing around all atoms, is just one of these. There are two more which are essentially just heavier versions of the electron, identical in every way apart from a bit fatter; these are the Muon and Tau (just fancy Greek names). It is the electron and its next heaviest version the Muon which we see in Super K travelling faster than the speed of light (see Faster Than Light post).

So when looking for neutrinos we see nothing coming in (the neutrino sneaks in like a Ninja) and then suddenly there is a charged particle born travelling faster than light in water. This particle creates light which is turned into electricity by our inverse light bulb electronics and fed to computers where we build up a picture of what went on.

This has been a bit of a long post, I apologise, but it is difficult to get a nice contained post without going into some of the detail around neutrinos. Next post I will talk about electrons and Muons in Super K.

For Now It's Goodbye Protons and Hello Neutrinos

2010-11-04T14:28:00.000Z

As the LHC (Large Hardon Collider) at CERN in Geneva powers down for maintenance another particle physics experiment in Japan is starting to power up once more. The T2K (Tokai 2 Kamioka) experiment is however a little different to the LHC. Instead of using protons directly T2K is using particles, building blocks of Nature, called Neutrinos. Neutrinos are ghostly things which cannot be seen by any of the experiments that are part of the LHC. T2K is therefore filling in parts of the picture of Nature that the LHC cannot.

LHC (Large Hadron Collider), CERN, Switzerland

These huge atom smashers require phenomenal amounts of electricity to power magnets and other electronics. While electricity is at it's most expensive/in demand during winter in Switzerland it is the opposite in Japan. Where the Swiss require heating for cold winters the Japanese have a thirst for air conditioning to make the hot humid summers a little more bearable. For this reason many of the experiments at CERN have a winter shutdown and the Japanese experiments a summer shutdown. During these times essential repairs are made to the sophisticated equipment which comprise the behemoths.

J-PARC (Japan Proton Accelerator Research
Complex), Tokai-mura, Japan

The Winter shutdown for the LHC is upon us the Summer shutdown for the T2K (Tokai to Kamioka) experiment, which began in June, is now coming to and end. After it own upgrade T2K will start once again start producing Neutrino particles in their trillions, firing them 295km across Japan to be measured by a whole array of particle detectors.

Both experiments are poised to take us into new frontiers of understanding our Universe. They are not in competition but instead complement one another by focussing on different and immutable parts of the same puzzle. 2011 is going to be an exciting year.

There is more information about Neutrinos and the T2K experiment in this blog and on my website, I will be talking more about them in my future blog posts too.

Faster Than Light.

2010-11-03T12:22:00.001Z

*My Comments on the September 2011 neutrino faster than light results*

Last post I talked of the massive tank of ultra pure water that is Super Kamiokande. So how do we see things in SK? What are we looking for? I mentioned the side of the tank is covered in inverse light bulbs turning any light produced in the water into electricity, which we read out with our computers and reconstruct what went on.

But where does the light come from? Super K is kept in complete darkness. The only light comes from charged particles travelling faster than light in the water.

Wait a minute.
Faster than the speed of light.
But I thought that nothing could travel faster than light.

This is true in empty space, a vacuum or air (which is a good approximation of empty space). Here light reaches the natural speed limit of the Universe, which we give the symbol c, equal to about 300,000 kilometres or 186,000 miles per second.

Change in the speed of light can be seen with a straw
in water. From Wikimedia Commons.

In water light is slowed down, so that it can actually only travel around 3/4 of the speed it does in air or empty space. This slowing of light can be seen in action by putting a straw in a glass of water or your favourite clear soda. You will notice that there seems to be kink in the straw where you go from the air to the liquid; this is because the speed of light, and therefore the fastest path for light to reach your eyes, is differnt in air and water. Because of this effect it is not against the laws of nature for use to produce thing travelling faster than light does in water, such as 0.8c (80% the speed of light in empty space).

When things with an electric charge (such as the electron which is being pumped around your computer or phone to power it right now) travels faster than light in water then we get a very interesting thing happens.

You may have heard of something called a sonic boom. This is a loud explosion of air that happens when anything travels faster than the speed of sound through air. Cutting it's way through the sky, a jet fighter plane it is constantly pushing air out of it's way at airs natural speed, the speed of sound. The problem comes as the jet reaches this same speed; the air cannot get out of the way of the plane fast enough and so begins to bunch up and build up in pressure (energy). As the plane crosses the sound barrier, and travels faster than the speed of sound in air, then this pressure (energy) build up is released as a huge explosion.

F18 Fighter Jet breaking the Sound Barrier.From Wikimedia Commons.

Cherenkov Radiation in a Nuclear Reactor.From Wikimedia Commons.

This "Sonic Boom" was the reason that Concorde, when flying it's fast London/Paris to New York run, could only hit top speed when over the Atlantic. If it had done so over populated areas it would have wreaked havoc with windows below.

The same thing occurs when things with electric charge travel faster than light can. When I say a particle has a certain electric charge, take the negatively charged electron for example, all I am saying is that that something is constantly telling the world around it that "I exist and if you come in to contact with me you must treat me in this manner". This information which is constantly streaming from anything with an electric charge tells other electrically charged things, as well as electric and magnetic fields, that if you come within the personal space then you should treat me like this: bend me this way in a magnetic field or repel me is you too have the same like charge.

Build up of electromagnetic information results in light going outward in a cone.
From Wikimedia Commons.

Instead of air bunching up as it does with fighter jets it is this information, streaming out at the speed of light within water, that bunches up and builds up in energy (pressure). This energy is released as light, a visible (optical) version of the Sonic Boom. Instead of hearing it we see it, with our inverse light bulbs. This effect is called Cherenkov radiation.

The light comes out in a cone and casts great circles or rings on the side of Super K which can be recosntructed from the 1000's of electronic eyes covering the walls.

Next Blog: Particles and Super K.

The Super K in Super K Sonic Booooum!

2010-10-29T11:48:00.000+01:00

Super Kamiokande (Super K for short) is a real piece of scientific equipment, a particle detector, located underneath 1km of rock at the heart of Mount Ikenoyama in Gifu prefecture in western Japan. It is a massive cylinder as tall as a 14 story building (40m) and the same in diameter. Looking into this cathedral sized cylinder are 11,146 electronic eyes called photo multiplier tubes (PMTs) attached to the walls. Essentially inverse light bulbs, turning light into electricity rather than the other way around, each of these PMTs are whopping 50cm (20") in diameter.

The Super Kamiokande detector, re-filling with water after the 2006 upgrade.

This vast space is filled with over 33 Olympic sized swimming pools worth (50,000 tonnes) of ultra pure water. The water is so pure in fact that if you were to put your hand in it you would lose all of the naturally occurring salts and oils in your skin leaving it bone dry. The reason for the purity is that we require light to be able to travel the entire distance through the water to reach our electronics on the walls. Any impurities dissolved, like the stuff you see on the back of your bottle of mineral water, would scatter the light on it's journey to the electronics and reduce the amount we see.

So light from particles travel through the massive amount of ultra pure water, enter our inverse light bulbs and is turned into electricity which is channelled to our computers to build up a picture of what is going on in Super K.

Next Blog: Faster than light.

Penultimate

2010-10-26T20:07:00.001+01:00

Tomorrow is our final day and I don't want it to end. Each day I have lost track of time in either the boat or lecture room of the darkened John Dalton workshop. Each hour racing by as if minutes. Time flying as I get into discussions, answer questions, talk about physics and give science boat tours. Not my normal 9 'til 5, not that it even exists for physicists.

Once more to the boat, once more to the talk. Once more to tentative audiences hanging on my words, surprised and amazed with the booooum and the light. Once more I will miss my lunch, forget my hunger and push on through. Once more I will have the privilege to talk of ghosts, faster than light and the creation of it all.

Once more I will wear my white Tyvek suit. Come and join us before we are gone.

Dr Ben Still

Build it and they will come...

2010-10-25T11:45:00.000+01:00

We have had over 250 visitors through the doors of Super K Sonic Booooum this weekend and with a busy start to the day today, when we open at 2pm, we hope to continue string right through to Wednesday. If you have been one of the lucky through our doors we would love to hear about your experience. Leave us comments or questions on this website or contact us directly. If you have not visited yet it is not too late to buy tickets through this site or just drop by to see us in the John Dalton building, M1 5GD; we are open from 2pm-9pm today (Mon), 11am-4pm tomorrow (Tues) and 2pm-9pm in our grand finale on Wednesday.

We have had a brilliant team of volunteers helping us out and I would like to thank you all for your hard work, managing all the people visiting and joining in with boat and rope pulling duty. The photo attached to this blog was taken after our triumphant first day with just some of these volunteers alongside the scientists, technical crew and the design director Nelly.

I look forward to seeing and talking with many more people, answering questions and transporting them to Japan to talk about particle physics.

Dr Ben Still

The Weekend

2010-10-25T00:28:00.000+01:00

And so ends a long weekend. Long but rewarding. I have had an incredible amount of fun talking about science with many different people this weekend. I have received some brilliant questions. Taken members of the public to a mine underneath a mountain in the West of Japan. Discussed the life and death of stars, the creation of the entire visible Universe and the symmetrical laws that govern it. All of this from a disused workshop in Manchester.

From a girlfriend surprising their boyfriend to families on a day out, all seem enthralled by the sights, sounds, atmosphere and science of Super K Sonic Booooum. Wowed by the experience all seem to discover something new about the Universe in which they live. Maybe the fact that it is all made from just twelve building blocks or that light travels slower in water than in air. Whatever the message taken away I hope it raises questions, questions that were not there before.

Three more days and I hope many more questions and intrigued people to follow.

Dr Ben Still

Super K Sonic Booooum!!!! : Construction II

2010-10-19T15:19:00.000+01:00

We were interrupted for a short while this morning by a fire alarm in which we all experienced the famous Manchester rain. Damp Manchester, I am reliably informed, is the reason for the cotton industry being based here as it kept the cotton moist. After getting back in the dry I get into the Super K pool, wading further and further into the centre hanging balloons.

Lunch time now and we have installed half of the balloons (PMTs) in the Super K Sonic Booooum tunnel! We string them together and then hang them on the wire support structure. We have a production chain Balloons - > Strings -> Tunnel and it is working like clock work, we hope to finish the tunnel by the end of the day.

It is looking so good and, as a famous particle physicist once sung, things can only get better.

Super K Sonic Booooum!!!! : Construction I

2010-10-18T22:32:00.000+01:00

I arrived in an unusually dry Manchester today carrying my box of 50 Tyvek suits and rucksack of clothes for my 2 weeks on the road. I entered the John Dalton building at MMU, where Super K Sonic Booooum is being installed, and was amazed at how far the construction had developed.

The water pool and boat rails were in place and the net tunnel constructed in three days of hard work and the technical talents of Andrea Salazar, Lee Jones and Hugo Sterk. After a quick video conference meeting I spent the rest of the afternoon with a group of brilliant volunteers who helped us blow up 800 balloons (PMTs ) today, thank you all!

The first 5 strands of balloons have been fixed to the net tunnel as the installation takes shape. We now wait on crucial supplies of tape before we continue with the hanging of the other balloons. Tomorrow promises to be very busy with 200 more balloons arriving and almost all 1000 to be strung and hung.

It is certainly a change to a day in the office programming at my desk.

Dr Ben Still

Ready to Measure Ghosts

2010-10-06T11:58:00.000+01:00

The last piece of the Tokai to Kamioka experiment in Japan was put into place this morning. The experiment is now poised to look at some of the most ghostly things in Nature who may have the answer to the creation of our Universe.

This morning I received the brilliant news that construction of the Tokai to Kamioka experiment, T2K for short, is now complete. T2K will be looking at neutrinos, some of the indivisible building blocks that are used by Nature to construct our Universe. There are just twelve of these building blocks (see red and green blocks in the picture below).

The Fundamental Particles

The Large Hadron Collider (LHC) experiments at CERN (Geneva, Switzerland) cannot see any of the three neutrinos (bottom row green blocks) directly. We therefore require specialised experiments to understand neutrinos and complete our picture of the Universe.

The reason the LHC experiments cannot see neutrinos is their ghostly behaviour. Seeing a neutrino is a rare occurrence despite being by far the most common of the previously mentioned building blocks. To give you an idea of how numerous and ghostly they are take a look at your thumbnail. Every second there are of the order 100 billion (100,000,000,000) passing through just your thumbnail each second, mostly from nuclear reactions in the Sun. If you then think of the billions of billions of neutrinos which will pass through your body in your lifetime, you would be lucky if just a single neutrino noticed you existed.

With odds like this how do we ever see neutrinos? I hear you cry. You can do one or both of two things: Increase the amount of stuff you look for a neutrino with and/or increase the number of neutrinos. The T2K experiment uses both or these principles. An intense beam of neutrinos are fired in short sharp bursts from the J-PARC particle accelerator lab on the East coast of Japan. A detector close to where the beam is created, the ND280 near detector, sees a handful (<10) of these neutrinos each burst of the powerful beam. These neutrinos then travel 295km to a massive detector under a mountain in the west of Japan called Super Kamiokande. This detector contains over 33 Olympic swimming pools of ultra pure water, a massive amount of stuff for neutrinos to interact with.

The 295km journey neutrinos take in the T2K experiment; from the J-PARC particle accelerator lab on the East coast of Japan through the ND 280 near detector (bottom right) to the Super Kamiokande detector underneath a mountain in the West.

The experiment has been running since April of 2009 but the near detector was missing big pieces of apparatus. These final particle detectors, called electromagnatic calorimeters (ECals), have now been installed and checked to confirm they work as designed. The ECals were designed and constructed here in the UK by scientists and engineers from six Universities (Imperial College, Lancaster, Liverpool, Sheffield, Queen Mary and Warwick) and two research labs (Daresbury and Rutherford Appleton).

The neutrino beam is switching on again in late November with more power and a fully loaded set of detectors. It won't be long until T2K sheds more light on the ghostly neutrino and reveals any secrets it may be hiding about our Universe.

Congratulations to Peter Kalmus!

2010-06-30T11:05:00.000+01:00

The brilliant Peter Kalmus has deservedly been made an Honorary Fellow of the Institute of Physics! He has received this for all of his pioneering, influential and wide-ranging contributions to physics and to science generally.

He joins 38 such Fellows who include 7 Nobel prize winners, 25 Fellows or Foreign Members of the Royal Society (with some overlap) and 15 Lords, Knights or Dames. The most recent Honorary Fellow was Steven Chu, Nobel Prize Winner and present United States Secretary of Energy.

I count myself lucky to be a part of the research group he has shaped and to have to opportunity of joining him for lunch most days when in London.

I have included the citation for his award below.

Peter Kalmus is a distinguished particle physicist. In 1977 his group at Queen Mary College London became part of a collaboration to design and build a large detector for the CERN proton-antiproton collider, which in 1983 played a key role in the discovery of the W and Z particles. These were the mediators required for the experimental verification of electroweak unification.

Peter received the Institute’s Rutherford Medal for his role in this discovery. He is the author of more than 200 papers. As well as his distinguished research, Peter has enjoyed teaching students at all levels. Physics outreach has become his major activity since his notional retirement. In recent years he has given 200 talks on particle physics to about 30,000 school pupils and others in the UK, Ireland, South Africa and India,

He has also been particularly active within the Institute, as a member of Council, Vice-President, and chair of the High Energy Physics Group, Education and Public Affairs Board, and London and South East Branch.

Link to IOP site

Win!

2010-06-26T09:04:00.000+01:00

I haven't had time to blog over the past couple of weeks because of lots of work but also because of taking part in the brilliant I'm A Scientist Get Me Out of Here. Two weeks of questioning from secondary school students about any and every aspect of science, being a scientist and life beyond.

In the 'Ask' a scientist section I have been fielding questions ranging from the light hearted 'What is your favourite Disney film?' to the deeper 'Was there anything before the Big Bang?'.

The live chats were crazy fast firing frenzies of questions, comments and quips. I received some great complements like 'I think ben should be made into a religion cos hes awesome at science'. Whether these were said in sarcasm or not I am taking them!

The whole thing was an amazing and intense learning experience; a crash course in science outreach. You speak to students of all ages and levels of interest. And some of the more imaginative questions really make you think, usually about the very fundamentals of your science which you may take for granted day to day.

My fellow scientists were tough competition, each extremely eloquent and passionate about science. So I was so happy after every eviction to find that the students voted for me to stay in the competition. After 4 days of evictions I was amazed to find I was the last scientist standing in the Sodium Zone, and crowned winner!

As I said on the website; If I get just one vote because a student has learnt something new or become excited by science then my job is done. But to win the competition makes me happy on a whole different level, because it hopefully means that many students feel this way. I hope I have been able to encourage them to continue to studying science and maybe see it in a new light.

I want to thank Sophia Collins and the whole team at I'm A Scientist for organising such an exciting event. Also thanks to my fellow scientists Louisa Chard, Heather McKee, Beth Dyson and Andre McKinley who made it a tough nail biting competition to the very end.

And most importantly thank you to the teachers and students of The Hazley School, Ryton Comprehensive, Perth Academy and Mangotsfield School for the challenging questions and fun chat.

If you want to checkout my I'm A Scientist profile, along with some of the questions I answered, click here. The I'm A Scientist press release announcing the winners is here. Queen Mary, University of London press release here.

I'm a Scientist

2010-06-15T21:48:00.000+01:00

Today I took part in my first online chat with secondary school students, as part of I'm a Scientist. The competition pits the wits of five or six scientists against school classes. The students can ask anything they want, a no holds barred access to real researching scientists. Students can also leave questions to us outside of live chats which we answer on our profiles.

The first week is a getting to know the scientist and the science. The second week it is voting time. Each day a scientist is voted off and the last of us standing is crowned a winner and is given £500 to spend on outreach activities.

Now back to the live chat. Overwhelmed is the best word to describe the experience. An onslaught of personal questions peppered with some great science questions. Below are some of my favourite questions and my answers:

Q: Who is your'Science Idol'?

A: Richard Feyman. Brilliant teacher, bongo player and hell of a ladies man.

Q: Do you prefer Biology, Chemistry or Physics and why?

A: Physics all the way (it is all physics in the end!)

Q: Ben, do you belive in the big bang

A: I don't think it is a case of believing in the Big Bang, there is lots of evidence for it!

Q: How does E= MC2?

A: Because when it comes to gravity energy and mass are the same thing

Q: What are the gravitational differences between black hole and a mini black hole?

A: Mini black holes exist only if there are many dimensions of space not just 3 and can only live for a fraction of a fraction of a second

Ready to Discover

2010-02-25T12:53:00.000Z

The Tokai to Kamioka (T2K) experiment in Japan may not use the phenomenal energies reached by the Large Hadron Collider (LHC) at CERN in Switzerland, but using different techniques it also gives a window to the early Universe. Yesterday the final piece of the T2K experiment fell into place as the Super Kamiokande (Super-K) detector saw it's first neutrino particle fired from a man made beam created 295 km away.

Neutrinos are one of nature's indivisible building blocks of the matter, which makes up everything we see around us. In fact they are the smallest of what we call the fundamental particles. They are ghostly; rarely interacting with other matter. Billions upon billions pass through your body every second yet you would be extremely lucky if just one of these noticed you in your entire life. Because of this the LHC cannot 'see' neutrinos in the huge spray of particles which occur when it smashes protons together. Seeing a neutrino is a game of chance. To improve the odds experiments can either increase the amount of matter that the neutrino can interact with or increase the number of neutrinos.

Increasing the amount of matter means massive particle detectors, and at 50,000 tonnes they don't come much bigger than the Super Kamiokande detector. The most intense man made beam of neutrinos ever constructed is fired 295 km at Super-K from the J-PARC facility on the East coast of Japan; a Japanese version of CERN with multiple particle accelerators. Before starting the long journey a set of other particle detectors give an understanding of the beam, a short distance after it is first produced.

When all aspects are combined together the T2K experiment will allow unprecedented access to the mysterious world of this particle which cannot be seen by other experiments. Super-K was the last element of the experiment to see a neutrino interact but it did so yesterday.

The first T2K event seen in Super-Kamiokande. Seen perfectly in time

with the arrival of a pulse of neutrinos from the J-PARC beam.

Now the stage is set. The players are ready. But there is no script. This is improv. Although we know the gist of the story we do not know how it is to play out or what the end will be. Almost everything we learn about this tiny ghoul of a particle challenges our previous ideas of how the Universe works on the smallest scales. T2K hopes to continue this trend, and may even be able account for one of the biggest mysteries of all: Where did all of this matter come from? Whatever the result may be, T2K is ready to discover.

Official press release here: English Japanese

Magnetic Fields and Particle Physics

2010-02-03T20:39:00.000Z

Magnets are an important part of any particle physics experiment allowing us to accelerate and analyse. The magnet used in the near neutrino detector of the Tokai to Kamioka (T2K) experiment has been recycled from a previous, Nobel Prize winning experiment, called UA1.

Currently (pardon the pun!) magnet has had a massive 2700 Amps of electricity running through it; equivalent to around 5,400 100W light bulbs switched on at once. This produces a magnetic field of 0.188 T (Tesla). This may not sound like a large number but this is over 3,700 times stronger than the average magnetic field of the Earth.

This magnetic field is necessary to bend the particles produced when a Neutrino interacts within our detectors, which are inside this magnet. The particles bend because they are electrically charged, oppositely charged particles bend in opposite directions. The amount a particle bends in a magnetic field and the energy it deposits as it ionises the sensitive detector allow us to determine the momentum of the particle.

This bending can be seen beautifully in the cosmic ray interaction taken by the detector just today.

Can photons create matter?

2010-01-29T10:05:00.000Z

I have just been asked by a friend if photons (particles of light) can create matter and I unashamedly used it to talk about my research. Here is my response:

Yes is the short answer.

A longer answer is that pure energy such as photons create equal amounts of matter and also anti-matter when we perform experiments using particle accelerators, such as the LHC.

This symmetry, of equal amounts of matter and anti-matter, posses a problem though because the Big Bang was a pure ball of energy. Eventually the equal amounts of matter and anti-matter the Big Bang energy created would find each other and form pure energy again; they don't mix well together. This would be a cycle of energy->matter/anti-matter->energy, ongoing until the Universe had cooled to a temperature where the energy of photons could no longer produce even the lightest of charged particle and anti-particle - the electron and the positron.

This would be a problem. Not only would the Solar system and galaxies not be able to form but the very fuel that stars burn to stay alive would not form. In short if this symmetry between matter and anti-matter were perfect then the Universe we see around us could not exist.

My research involves me searching for the imperfection of this symmetry using the smallest form of matter, Neutrinos. These indivisible elements of Nature give us a unique window into the bizarre world of particle physics. Neutrinos may hold the answer to the creation of the Universe.

Another Day Another Detector...

2009-12-20T01:02:00.000Z

Christmas came early today for myself and other scientists working on the Tokai to Kamioka (T2K) experiment in Japan. Over the past few months the experiment has been readying itself to detect the most elusive particles called Neutrinos. The science, to be performed by this experiment, is crucial to understanding how our Universe was created within a few short seconds after the Big Bang.
Neutrinos are one quarter of the indivisible constituents of the Universe in which we live, and believe it or not the most numerous; but I don't blame you if you haven't heard of them! They don't do very much at all, which means that they can't be used for everyday things, like electrons who transfer electricity which powers our modern life. Neutrinos almost entirely ignore everything around them. Seeing a Neutrino is a fools game of chance. To increase odds of capturing one in the T2K experiment we will fire the most intense man made beam of them all of the way across Japan.

The name of the experiment, Tokai 2 Kamioka or T2K for short, comes from the two towns in Japan where we have placed sensitive particle detectors. These detectors take a snapshot of the beam of Neutrinos through their interactions (as seen in the picture above).
In Tokai, where the Neutrinos are created, there are two sets of detector. Today the complex near detector, called the ND280, detected its first Neutrino from the beam. This is a huge landmark as the ND280 is the last piece of the T2K experiment to be readied for the science to begin in earnest early next year.
T2K will bring scientists closer to understanding the mysterious and ghostly neutrino which remains the least known piece of Natures Lego set from which our Universe is constructed. With this addition to our fundamental knowledge we hope to be able to determine the origin of, not only the Earth but, the entire Universe in which we live.

Why 2012 Will Not Happen!

2009-12-11T12:54:00.000Z

I am not talking about the London Olympic Stadium, which I can see being constructed from my office window, but instead the disaster portrayed in the latest blockbuster movie "2012".
The premise is that during a period of extreme solar activity particles called Neutrinos somehow mutate from interacting extremely rarely to very strongly with the Earth. The billions of Neutrinos from the Sun interacting with the core of the Earth causes it to heat and consequently the Earths crust to split and crack.

Here are a few Neutrino facts:

Neutrinos DO exist; they make up a quarter of Natures indivisible building blocks/particles
They ARE created in huge quantities in the Sun; in nuclear fusion reactions.
They indeed INTERACT very rarely with other normal matter; which makes up the Earth as well as you and me and the entire visible Universe.
They will NEVER mutate in the way suggested in 2012.

The way in which Neutrinos interact is a law of Nature which has existed since the dawn of time and so the idea that this would change during a solar flare is crazy. Many experiments using Neutrinos and other particles have been conducted and have helped us understand the way in which Neutrinos interact.
The experiment which I work on is the next generation of such experiment. We will be creating the most intense man-made beam of Neutrinos ever constructed. We will be firing this Neutrino beam directly through the Earth's crust a distance of 295km from one side of Japan to the other. This is only possible because the Neutrino interacts so rarely. The Earth, and all matter, is more transparent to Neutrinos than a pane of glass is to light.

Pre Budget Report

2009-12-09T15:54:00.000Z

Just had a look through Alistair Darling's Pre-Budget Report and am disgusted that the government hopes to claw back £600M from science research and higher education funding. The many other cutbacks seem reasonable such as the "£500 million from reducing spend on IT, including by reducing the cost and scope of the NHS IT programme;" considering the programme has been a botch since its first proposal.
In the same document where the £600M cut in science and higher education funding is proposed the government outline a plan to spend £325M on the innovation investment fund (IIF), a fund designed to exploit scientific and technological advances from research.
It seems obvious to me that a cut in science research funding will reduce the amount of scientific and technological advances; less resources and scientists equates to less progress. This would be true in all fields of scientific research; not just applied science but blue skies research too. Particle physics and astrophysics have developed many imaging and computing technologies. These have proven not only to have commercial value but have also improved the quality of our modern lives; from the way in which we communicate to medical imaging.
I think the IIF scheme is brilliant idea. I myself went on an entrepreneurship course run and funded by the faculty of science at a higher education institute. The outcome was great, a number of scientists that attended the course have already begun to exploit their research and make the government money. Others, such as myself, certainly know what to look for and how to go about doing so. I entirely agree that scientists should always have possible commercial exploitations of their research in their mind but this should NOT guide the science.
True science pushes the boundaries of human knowledge, and usually requires the development of new technologies. In the purist sense the applications of these new technologies and knowledge cannot be predicted beforehand. This would serve to defeat the purpose of research in the first place. If we could predict exactly what we are to expect then we are not pushing any boundaries at all, but at the most just leaning on them.
The ability to recognise the opportunities of new knowledge is an important one to invest in. But if there is no new knowledge then there can be no competitive edge and certainly no exploitation.

Almost There...

2009-12-09T10:43:00.000Z

With the next Tokai 2 Kamioka (T2K) beam test scheduled for next week the off-axis near detector, the ND280, is piece by piece readying itself for neutrinos. In the early hours of this morning we received great news that yet another one of the sub-detectors was working in harmony with those already installed. All of the separate sub-detectors in the ND280 have to be able to converse with each other within nano-seconds (ns, a billionth of a second) which is no mean feat.

The ND280 (above) is a mixture of particle detector types. The dominant detector technology is that of plastic scintillator; a plastic that emits light when charged particles pass through it, the light is guided into photosensitive electronics and the amount of light recorded. The Pi-Zero detector (P0D), Fine Grained Detectors (FGDs), Electromagnetic Calorimeters (ECals) and Muon Range Detectors (MRDs) are all examples of plastic scintillator detectors.
It was no easy task for my colleagues in Japan but last week they managed to get all of these detectors talking to each other and measuring the passage of cosmic ray muons. Muons are heavy versions of the electron that steam train their way through a large amount of matter leaving only small amounts of ionisation (stripping electrons from their host atom) which we use to see where it has been. This steam train can be seen in the event display below as it passes through the entire ND280.

These Muons were created through interactions of protons which hit the upper atmosphere and produce showers of particles including the Muon. These protons were not accelerated to high energies by the Large Hadron Collider (LHC) at CERN, but instead from astrophysical things such as the Sun or the death of a distant star.
The second detector technology is a time projection chamber (TPC), a box of gas which has a large electric field across it. A charged particle ionises the gas as it passes through the TPC. The electric field then forces the electrons, which have been stripped from the gas atoms, in a particular direction onto electronic readouts. Early this morning this pictures arrived in my inbox:

Another milestone has been achieved! The first TPC (blue box) talking to the other plastic scintillator detectors. Congratulations to all of my colleagues in Japan who are making brilliant progress on a daily basis. They are piecing together a set of extremely complicated electronics and detectors whose elements were constructed in many different countries across three different continents.

Bring on January and the full neutrino beam!

Missing Piece of the Puzzle...

2009-12-04T15:40:00.000Z

Frustration mounts as you are getting so close to completing the picture. You know where some of the remaining pieces of the puzzle should go but they do not seem to fit. Not only that but there also seems to be some missing all together. Some relaxing pastime this is turning out to be!

Particle physicists know this feeling all too well; we are trying to construct a picture of Nature at its most fundamental level, which is so close to being complete. However this picture, which we call the Standard Model, is still patchy here and there with things not sitting quite right and key pieces missing. Over the coming months the Tokai 2 Kamioka (T2K) experiment in Japan and the Large Hadron Collider (LHC) experiment at CERN in Geneva will start to complete more of this picture.

The Higgs: Just One Part of the Puzzle

One of the pieces which doesn't fit quite right is the Higgs particle; the giver of mass, or as some have dubbed it the God particle. Mathematics gives us the Higgs jigsaw piece and tells us vaguely what size it is and where it fits into the picture of Nature. But until we definitively see one we cannot place it down with confidence. The primary mission of the particle detectors (Atlas, CMS) at the Large Hadron Collider (LHC) is to photograph a Higgs in nature to help us understand it’s place in Nature.

Going Where The LHC Can't See

Some of the missing puzzle pieces the LHC detectors cannot help us with, in fact they are blind to them. Neutrinos are the most numerous but least understood of Nature's fundamental and indivisible building blocks.

Little is understood about Neutrinos because they interact extremely, extremely, extremely rarely with normal matter; the stuff from which the entire visible Universe is composed. Because we can only construct particle detectors from the normal matter materials around us, the neutrinos produced in the LHC are practically invisible as they almost never interact in their detectors.

So How Do We Know They Are there?

Seeing something as rare as a Neutrino is just a game of odds, you either increase the amount of matter you put in their path, make huge detectors, or increase the number of them passing through your detector. In the Tokai 2 Kamioka (T2K) experiment we have chosen to do both.

T2K increases the number of Neutrinos by creating a beam of them, the most powerful created by man. T2K also uses a massive 50,000 tonnes of pure water as a target in the Super-K detector. These two, combined with yet more detectors near to where the beam is created, will allow T2K an unprecedented look into the world of the Neutrino.

LHC vs T2K

It is not a competition. Both experiments are trying to answer related questions, just from different perspectives. When understanding most things in life we need many perspectives to determine its true form.

T2K, and other Neutrino experiments, are therefore equally important as their high-energy accelerator counterparts like the LHC. There may not be many doomsday stories, such as black holes, surrounding T2K, but the science it will produce will expand the horizons of human knowledge just as the LHC will giving us a richer picture of Nature and the origin of our Universe.

The bits about the Neutrinos that we understand are altering our perspective of the rest of the picture. It is an important task, therefore, to find the missing Neutrino pieces to understand if we are interpreting the current picture correctly. Neutrinos may also be the key to understanding how we have jigsaw pieces to play with in the first place.

For more info continue reading this blog or checkout my website.

Death, Birth and Beams.

2009-11-29T14:18:00.000Z

Here on the T2K (Tokai2Kamioka) experiment we begin our science in a chain of death and birth of particles.

The picture below was taken using a bubble chamber detector. Superheated liquid, heated well above it natural boiling point, is held in a pressurised container to prevent boiling. As a particle with electric charge passes through the liquid it deposits energy, in the form of ionisation where electrons are stripped from their atoms. This extra energy allows small bubbles of gas, boiling, to occur along the path of the particle, which is what can be seen in the photograph below.

The unstable (positively charged Pion) particle is the long arching (blue) curved track which after some time dies through decay and gives birth to a visible positively charge anti-Muon (green). Muons (anti-Muons), essentially overweight Electrons, are also short lived. In it's death the anti-Muon in the picture (green) goes on a serious weight loss programme through a decay producing a much lighter spiraling Positron (red), the electrons mirror anti-particle.

In the above picture you can see that there are sharp angles made in the tracks at each of these decay points; as we go from blue to green to red . This suggests there is more going on than we can actually see. Even if we take into account the mass loss of the particles, the momentum of the tracks is not conserved; which would be seen as a much smoother transition. The answer: other particles are also being born in these decays, particles without electric charge and therefore invisible to the bubble chamber. These particles are called Neutrinos.

The full chain of decay from the Pion to the final Positron is shown below, you can see that in fact three of these electrically neutral neutrinos are produced, each of a different type.

The first stage, the decay of the Pion, is used in the T2K experiment to produce a beam of Muon type neutrinos, , which we then use for our science.

Pions are produced in large numbers when a beam of proton, like the one circulating in the Large Hadron Collider in CERN, strikes a stationary target; the lighter the atoms the better. We use protons from an accelerator in Tokai, on the very East coast of Japan, and slam them into graphite, the same stuff in the core of a pencil, which is pure Carbon.

The Pions are then focused into a beam using large bell shaped horns which, when supplied with over 300,000 Amps of electricity, produce a powerful magnetic field to pull the Pions in a common direction (for comparison a normal household can only take 3 or 5 Amps!). The Pions then travel along a 110m tunnel in which they decay to Neutrinos and Muons just as in the bubble chamber picture above.

The diagram above shows the chain of Neutrino beam creation in the T2K experiment; Protons -> Pion beam -> Neutrino beam. The neutrinos beam first encounters a collection of neutrino detectors at 280m from the proton target, which I will talk a lot more about in future blogs.

As hard as we try we cannot produce a 100% pure Muon Neutrino beam, although it is over 99% . Some electron neutrinos are produced, rarely from the decay of Muons as in the bubble chamber picture above. are also created in the death of other particles called Kaons, produced alongside the Pions when colliding the protons with the pencil graphite target. As I will explain in future blogs, it is extremely important that we understand accurately how many electron neutrinos we are producing is we are to make new science measurements.

This is just the start of a 295km journey across Japan for the Neutrinos, in which they are going to misbehave. It is their lack of respect for the normal particle behaviour that allows scientists to tell more about the very creation of our universe from the fundamental particles it consists of. Please keep reading as I explain more about Neutrinos and the important roles they play in the creation and sustenance of the Universe, and ask lots of questions!

Beaten to the punch!

2009-11-26T16:40:00.000Z

Tokai 2 Kamioka (T2K) beat the Large Hadron Collider (LHC) by a day to detect it's first particle interaction!

On Monday the Atlas detector saw evidence for the first collisions of the two beams of protons, which travel in opposite direction around the 27km circumference of the LHC, at CERN in Geneva (http://bit.ly/8U6DVX). But on Sunday however my colleagues manning the near detectors of the T2K experiment saw the first interaction in the Interactive Neutrino Grid (INGrid) detector (see image) beating the LHC by a day in the race for data (http://bit.ly/4RyvZK).

Just as with the LHC experiments, this would not have been possible were it not for years hard work by many scientists and engineers from all over the world.

Both the LHC and T2K are doing complementary science, with T2K picking up where the LHC experiments leave off and visa versa. The LHC will be using phenomenal energies to probe possible unknown interactions between the fundamental particles. T2K on the other hand will be using much more modest energies, still probing these interactions but by focusing on the strange properties of the fundamental particles called Neutrinos, which cannot be seen by the LHC detectors.

In the coming days I will attempt to talk more about particle physics focusing on the neutrino: what is it and why are we interested in it and where does the T2K experiment come in.