Experimenting with MICE, on the grid

Thu 8th April 2010

While the LHC reaches for the highest energy collisions ever generated by humans, other scientists are looking in other directions. At the Rutherford Appleton Laboratory (RAL) in Oxfordshire the Muon Ionization Cooling Experiment (MICE), a collaboration of particle physicists and accelerator physicists, is building a key element of a new type of physics experiment, a neutrino factory, and they are using the Grid to understand it.

One of the biggest questions surrounding the Big Bang is why was more matter created than anti-matter. No one is complaining, this asymmetry has led to our current universe, however theory says that they should have been created in equal measures. This would have resulted in each cancelling the other out but more matter was created than antimatter leaving us with the universe we now know. This glitch in the theory is called CP violation and there are many experiments around the world trying to investigate it. Some physicists studying the problem are using neutrinos but to make the next step in this field they need to be able to create a lot on demand, they need a neutrino factory. MICE is the first step in this process. Dr Ben Still of the T2K experiment recognises the need for these new technologies “The new generation of experiments, like T2K, will rapidly improve our understanding neutrino physics. However, to understand the neutrinos role in the creation of the Universe and its place in nature we will need neutrino factories and MICE is an important step towards building one.”

MICE is the foundations for a neutrino factory. The theory of creating a beam of neutrinos is relatively well understood. Accelerate a beam of protons at a material target (for example, a mercury jet ), this creates a beam of sub atomic particles called pions which decay further into a beam of muons which can be captured and will further decay into neutrinos. However once the muon beams are created they’re far too large to fit in a neutrino factory, where they will decay to produce neutrinos. Being able to create a dense beam of muons propagating parallel to each other will be essential in creating a viable neutrino factory. To do this the Muon beams need to be “cooled” down i.e. reduced in transverse size.

The Standard Model showing the three kinds of Neutrino; muon, electron and tau

Cooling a beam of particles isn’t something new and physicists have been using a method called stochastic cooling for years. However this takes many hours to work and a muon lasts only 0.0000022 seconds before decaying. Therefore, MICE plans on using a different method, ionisation cooling. This works by passing the muon beam through low density absorbers, which reduce the momentum of the beam, while ensuring the particles are all travelling in the same direction. This beam is now re-accelerated by Radio Frequency cavities to the required energy with the effect of reducing the transverse size of the beam.

Schematic of the MICE cooling channel

Between January and September of last year the team used over 60,000 hours of grid computing time, running tens of thousands of simulations of the muon beam. This not only proved that MICE will be able to carry out muon cooling measurements to the required accuracy but also that MICE only needs to run for a 10th of the time thought necessary from initial studies.

The work was carried out by David Forrest, a PhD student at the University of Glasgow. “The Grid has enabled us to carry out tens of thousands of simulated experiments in a short space of time. Without the massive computing resources made available through the Grid, this part of the study would not have been feasible.”

The work will be published by AIP in its proceedings of NuFact09: The 11th international Workshop on Neutrino Factories, Superbeams and Beta Beams.

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