Muon capture in hydrogen and deuterium

Abstract

We report on a new generation of muon lifetime experiments at PSI to measure the nuclear muon capture rate in hydrogen and deuterium with ≤1% accuracy. The goals are to determine in μp capture the induced pseudoscalar coupling g _P predicted in HBchPT, and in μd capture the axial two-body current term L_1A described by modern EFT’s. For the μp experiment a hydrogen TPC was developed as active muon stop detector, surrounded by cylindrical wire chambers and a plastic hodoscope as electron detector. Ultra-high purity of the hydrogen isotope $^1H_1$ at levels below 10^− 8 was achieved with a specially developed gas circulation and purification system, and with a novel isotope separation column. About 2 ·10¹⁰ events were collected which are now in final analysis. Data from the first production run result in g _P = 7.3 ± 1.1 in good agreement with theory. The μd experiment is in development. It requires measurements in ultra-pure, cold deuterium gas at ∼30K. For this we are constructing a new Cryo-TPC.