The Neutron Decay Facility PERC: High Precision Spectroscopy and Near Perfect Spin Transport

by Karina Bernert (Technical University of Munich)

Thursday 25 Jan 2024, 09:30 → 11:00 Europe/Berlin

E18 Seminar Room

Measurements of free neutron decay enable a variety of tests of the Standard Model of particle physics. Among the observables are the parity-violating beta asymmetry A, i.e. the angular distribution of the beta particles with respect to the neutron spin, and the Fierz interference term b.
The new PERC (Proton Electron Radiation Channel) facility is being set up at the research reactor FRM II of the Heinz Maier-Leibnitz Zentrum in Garching, with the aim to measure correlation coefficients one order of magnitude more precisely. PERC's central component is a 12 m long superconducting magnet system. It hosts an 8 m long decay region with a uniform field. Here, a neutron guide keeps the beam divergence minimal and for this PERC crucially requires low-depolarizing neutron mirrors at the level of 10⁻⁴. To minimize systematic uncertainties, an additional high-field region selects the phase space of electrons and protons that can reach the main detector. In addition to the main detector, PERC also features a secondary detector system to identify backscatter events.
I give an overview of PERC and the progress of its setup, and details to the design of the backscatter detector system. Additionally, I show preliminary results of a measurement campaign at the ILL PF1b beam line last summer, in which we used the Opaque Test Bench setup to determine the depolarizing effect of CuTi supermirrors.