This proposal is for instrumentation development needed for the Muon Ionization Cooling Experiment (MICE). In the field of particle physics, there is increasing interest in using particle accelerators to form very intense beams of high-energy muons. Discovered in 1937, the muon, a more massive "cousin" of the electron, is a subatomic particle whose simple and well-understood interactions with matter make it a useful probe for a range of purposes. Until now, however, due to its short average lifetime of 2.2 microseconds, it has not been possible to accelerate muons. The key step in demonstrating the feasibility of muon accelerators is the Muon Ionization Cooling Experiment (MICE). The main obstacle to accelerating an intense muon beam is that such beams are created too large to fit into the typical vacuum chamber of a synchrotron and the short muon lifetime leaves little time to adequately shrink the beam. Ionization cooling is a new technique to shrink, or "cool" a muon beam quickly. In this process, a beam of muons passes through carefully selected material in which it loses energy by ionizing nearby atoms. These interactions reduce all three components of a muon's velocity: horizontal, vertical, and longitudinal. The muon beam is then accelerated by radio-frequency cavities, replacing only the longitudinal velocity component of the muons. As the horizontal and vertical components are increasingly reduced while the longitudinal component is maintained, the muons' trajectories become more nearly parallel, allowing focusing magnets to substantially reduce the size of the beam. In practice, the ionization cooling process described above is complicated by multiple engineering challenges. For example, the beam must be contained in large-volume, high-field superconducting magnets, and the atoms of the energy absorbing material must be light (preferably hydrogen) so that the muons do not scatter so much as to overwhelm the cooling effect. The goal of MICE is to build a section of an ionization-cooling channel, instrument it to measure its cooling performance, and use a muon beam produced at a particle accelerator to demonstrate this advanced accelerator technique. The MICE project is a collaborative effort of some 150 physicists and engineers from Europe, Japan, and the US. MICE is approved and scheduled to run at England's Rutherford Appleton Laboratory. The $50 million estimated cost of the experiment is to be shared among the institutions of the collaboration.
