Ionization cooling is a key enabling technology for future facilities based on the acceleration and storage of muons. These include the Neutrino Factory, the ultimate tool conceived of for investigating leptonic charge parity symmetry violation, and also the Muon Collider, a facility offering a route to multi-TeV lepton anti-lepton collisions at the energy frontier.
Cooling refers to shrinking a particle beam's size, in both position and momentum space, in order for it to be efficiently matched into other beamline components, or to create small cross section for particle collisions. The muon rest lifetime however is a few millionths of second, meaning traditional beam cooling techniques are simply not quick enough to be useful. This motivates ionization cooling, a new technique with the potential to cool muons in the time required. Ionization cooling involves passing a beam of muons through some absorber material, typically liquid hydrogen, so that it lose energy and momentum in all directions, via ionisation of medium. This momentum is then replaced in the direction of the beam only, effectively shrinking the beam size in phase space.
The Muon Ionisation Cooling Experiment (MICE) is designed to demonstrate ionisation cooling for the first time. It is based at Rutherford Appleton Laboratory, U.K., but is formed of an international collaboration from many countries, including Japan, the U.S.A., Italy, Bulgaria, Switzerland and more. The High Energy Physics group at Imperial College plays a leading role on MICE, in particular supplying the high precision scintillating fibre trackers, used to measure the beam phase space size, both before and after cooling. More information about MICE can be here.