PRISM/PRIME
Advanced Muon Beam and the Experimental Search for Coherent µ-e Conversion with Sensitivity to the Branching Fraction of 10-18

Dr. Masaharu Aoki
Osaka University, Japan

PRISM is a project to build a Phase Rotated Intense Slow Muon source capable of providing a high-purity beam of µ± at 1011-1012 muons/second; an intensity nearly four orders of magnitude greater than any existing or currently planned facility. The designed central beam momentum is with very low dispersion, ±2% , a feature critical to reducing target-related backgrounds in the PRIME experiment. PRIME (the PRIsm Muon-Electron conversion experiment) is a one-of-a-kind experiment to directly detect the rare, and as yet unseen, process µ-N to e-N, coherent conversion of a muon into an electron in the field of a nucleus. A variety of extensions of the SM aimed at grand unification that involve supersymmetry or extra dimensions suggest the branching fraction for coherent conversion relative to muon capture on the nucleus to be only a few orders of magnitude below current measured branching fraction limits: 10-12 - 10-13.  With a targeted sensitivity of one event in 10-18, PRIME will be a powerful probe of the Standard Model (SM) of elementary particle physics.  Detection of this process would provide direct evidence of lepton flavor violation in the charged lepton sector, an unambiguous discovery of physics beyond the SM.  Even a null result imposes strong restrictions on many theories of grand unification. PRISM is currently under construction at J-PARC at the KEK laboratory in Japan, and PRIME is planned to begin taking data in approximately 2010.