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Neutrino beams are conventionally created by smashing protons into a target. This interaction generates a shower of pions which are then allowed to decay creating neutrinos in the process. Building such a beamline is relatively straightforward but we don't understand the pion production process well enough to fully understand the resulting neutrino beam.

A different idea is to try to use muons. These decay to neutrinos as well, in a well-defined and calculable way and is the basis of the Neutrino Factory - a facility which would better the quality and understanding of neutrino beams by more than an order of magnitude. It does this by generating pions, just like the current facilities, but instead of keeping the neutrinos, it keeps the muons from the pion decay. These muons are then passed into the accelerator where they decay to neutrinos. Useful thought this is, muons are difficult to deal with in an accelerator. Their short lifetime means you need to get them from their production point into some sort of accelerator very quickly and with minimal loss. Hence, you need to ensure that they are going in the right direction with the right velocity when they are injected into the ring. The technology does not yet exist to do this properly and there is a lot of work going on to test the different concepts of the accelerating channel.

One of the main parts of the channel is the so-called "cooling channel". This takes muons coming in with a large range of angles and energies from the pion decays, and focuses them so that they go in the right direction with a narrow range of momenta. One cannot do this with magnetic fields (as one does for electron beams) due to the heavy nature of the muon, so we need some other method. The method we are testing is called "Ionisation Cooling'. This method passes muons through carefully selected sections of material. The material slows them down, and then the are accelerated on one direction by RF cavitites. Repeated a few times, one can transfer the initial transverse momentum of the muons into longitudinal momentum.

This procedure, although it sounds feasible, has never been performed before. The MICE (Muon Ionisation Cooling Experiment) at the Rutherford Appleton Laboratory has been designed to implement a small section of this cooling channel to test whether this procedure works, and look at the areas which present problems in construction or operation. Warwick is part of this experiment. We work on the tracker - the most important part of the experiment.

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