Erlangen 2026 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 42: Fundamental Symmetries II

HK 42.3: Talk

Thursday, March 19, 2026, 17:15–17:30, AM 00.021

Status of the neutron decay experiment PERC — •Lilli Löbell — School of Natural Sciences, Technische Universität München, Germany

The decay of free neutrons is a powerful tool for precision tests of the Standard Model of particle physics. Correlation coefficients - such as the beta asymmetry A and the Fierz interference term b - serve as input for the determination of the CKM matrix element V_ud and for searches for (effective) scalar and tensor as well as right-handed couplings.

The neutron decay spectrometer PERC (Proton Electron Radiation Channel), which is set up at the research reactor FRM II in Garching, Germany, aims to improve the accuracy of several correlation coefficients by up to one order of magnitude. PERC consists of a 12 m long superconducting magnet system, in which the neutron beam is contained by a non-depolarizing neutron guide. The magnetic field guides electrons and protons produced in the neutron decay towards the main detector, which will initially be a scintillation detector with photomultiplier tube readout and later be upgraded to a silicon detector. A second detector system, which consists of a scintillator read out by silicon photomultipliers, is installed in the upstream area of PERC and allows to identify backscatter events. First measurements are planned for the end of 2026 after the restart of the FRM II.

The talk gives an overview of PERC and presents the current status.

PERC was supported by the Priority Program SPP 1491 of the DFG and the cluster of excellence ”Origin and Structure of the Universe”.

Keywords: neutron decay; weak interaction; CKM matrix