MuCap: Muon Capture on the Proton

Abstract

The singlet muon capture rate \Lambda_SΛS on the proton \mu^-\ p \to \nu_\mu~nμ−p→νμn is determined in a high precision lifetime measurement. The main apparatus consists of a new hydrogen time projection chamber as muon detector, developed by PSI, surrounded by cylindrical wire chambers and a plastic scintillator hodoscope as electron detectors. The parameter \Lambda_SΛS is evaluated as the difference between the inverse \mu\,pμp lifetime and that of the free \mu^+μ+. The result \Lambda_S^\text{MuCap} = (715.6 \pm 5.4^\text{stat} \pm 5.1^\text{sys})\,\text{s}^{-1}ΛSMuCap=(715.6±5.4stat±5.1sys)s−1 is in excellent agreement with the prediction of chiral perturbation theory \Lambda_S^{\chi\text{PT}} = (715.4 \pm 6.9)\,\text{s}^{-1}ΛSχPT=(715.4±6.9)s−1. From \Lambda_S^\text{MuCap}ΛSMuCap a recent analysis derives for the induced pseudoscalar coupling g^\text{MuCap}_p = 8.23 \pm 0.83gpMuCap=8.23±0.83 whereas \bar{g}^{\chi\text{PT}}_p = 8.25 \pm 0.25g‾pχPT=8.25±0.25.