The PRISM/PRIME Project

Lepton Flavour violation is predicted by many theories beyond the standard model. In the muon sector such a violation entails not only direct μ→eγ decay but also the conversion process μ→e. To measure this to high precision requires a large number of muons of very similar energy, and this is difficult to achieve from a muon target with conventional beam optics. PRISM is an FFAG system designed to accept large numbers of muons (1012/sec) with a wide range of energies, and render them monochromatic by accelerating the less energetic muons and decelerating the more energetic ones. To preserve Liouvilleʼs theorem, this is accompanied by a broadening in the timing of the muons, hence the name ʼPhase Rotated Intense Slow Muon source.ʼ The principles of this device have been demonstrated and components prototyped. PRIME is a detector (PRISM Muon Electron Conversion) which has been designed to stop 20 MeV bunches of muons in a thin foil, giving a very clean signal and reaching a background sensitivity of 10−18, four orders of magnitude better than todayʼs limits and probing the interesting region for BSM theories.