Speaker
Description
The instrument PERKEO III was used to measure most precisely the beta asymmetry in neutron decay at the cold neutron beam line PF1b of the ILL, Grenoble. From this measurement, we extract the ratio of nucleon axial-vector and vector couplings. When combined with the neutron lifetime, this provides the CKM matrix element $V_{ud}$ with only a factor two in precision to the combined result from superallowed nuclear decays. PERKEO's successor, the PERC instrument, is currently being commissioned at the FRM II, Garching, which aims at an improved measurement of the beta asymmetry by a factor of five. Pulsed neutron beams are key to eliminate or control systematics in both experiments. The inherent pulse structure at the proposed ANNI beamline at the ESS, Lund, will increase statistics by more than an order of magnitude for these measurements.
In this talk, I will discuss recent results by the PERKEO III collaboration and present the status of its successor PERC.
