Neutron decay with PERC: A progress report

The PERC collaboration will perform high-precision measurements of angular correlations in neutron beta decay at the beam facility MEPHISTO of the Forschungs-Neutronenquelle Heinz Maier-Leibnitz in Munich, Germany. The new beam station PERC, a clean, bright, and versatile source of neutron decay products, is designed to improve the sensitivity of neutron decay studies by one order of magnitude. The charged decay products are collected by a strong longitudinal magnetic field directly from inside a neutron guide. This combination provides the highest phase space density of decay products. A magnetic mirror serves to perform precise cuts in phase space, reducing related systematic errors. The new instrument PERC is under development by an international collaboration. The physics motivation, sensitivity, and applications of PERC as well as the status of the design and preliminary results on uncertainties in proton spectroscopy are presented in this paper.