Measurement Of Muon Capture On The Proton To 1% Precision And Determination Of The Pseudoscalar Coupling G(P)

The MuCap experiment at the Paul Scherrer Institute has measured the rate Lambda(S) of muon capture from the singlet state of the muonic hydrogen atom to a precision of 1%. A muon beam was stopped in a time projection chamber filled with 10-bar, ultrapure hydrogen gas. Cylindrical wire chambers and a segmented scintillator barrel detected electrons from muon decay. Lambda(S) is determined from the difference between the mu(-) disappearance rate in hydrogen and the free muon decay rate. The result is based on the analysis of 1.2 x 10(10) mu(-) decays, from which we extract the capture rate Lambda(S) = (714.9 +/- 5.4(stat) +/- 5.1(syst)) s(-1) and derive the proton's pseudoscalar coupling g(P)(q(0)(2) = -0.88m(mu)(2)) = 8.06 +/- 0.55. DOI: 10.1103/PhysRevLett.110.012504