Muon storage rings have the unique potential to be a clean source of muon and electron neutrinos and to offer a path towards the highest energy lepton colliders. The main challenge associated with those facilities is the development of an operational front-end muon cooling channel. A muon beam produced from the decay of pions does not naturally fit the acceptance of an accelerator without prior reduction of its emittance. The international Muon Ionization Cooling Experiment (MICE) collaboration is set to experimentally demonstrate the viability of ionization cooling as a means to increasing the muon beam brightness. The position and momentum reconstruction of individual muons in the MICE trackers allows for the development of alternative figures of merit in addition to beam emittance. Contraction of the phase space volume occupied by a fraction of the sample, or equivalently the increase in phase space density at its core, is an unequivocal cooling signature. Singleparticle amplitude and nonparametric statistics provide reliable methods to estimate the phase space density function. These techniques are robust to transmission losses and nonlinearities, making them optimally suited to perform a quantitative cooling measurement in MICE. Preliminary results are presented and possible opportunities are discussed.
Miriam Diamond