# Physics of fundamental Symmetries and Interactions - PSI2019

20-25 October 2019
PSI
Europe/Zurich timezone

## Measurement of the nucleon axial coupling in neutron beta decay

22 Oct 2019, 09:00
30m
WHGA/001 - Auditorium (PSI)

Invited Talk

### Speaker

Bastian Märkisch (Technische Universität München)

### Description

Precision experiments on neutron beta decay are used to determine the CKM matrix element $V_{ud}$ and to search for novel scalar and tensor couplings beyond the axial-vector and vector couplings of the standard model. In this presentation, I will discuss the result of PERKEO III on the parity-violating beta asymmetry obtained using a pulsed cold neutron beam at the ILL. The result confirms recent measurements of the nucleon axial coupling with improved precision. In consequence, it largely rules out dark decay channels as an explanation of the persisting discrepancy between the beam and bottle methods to measure the neutron lifetime. I will discuss implications on $V_{ud}$ from neutron decay and limits on scalar and tensor interactions. The status of the successor instrument PERC at the MLZ will be presented.

### Primary author

Bastian Märkisch (Technische Universität München)