Measurement of muon capture on the proton to 1% precision and determination of the pseudoscalar coupling gP

The MuCap experiment at the Paul Scherrer Institute has measured the rate Λ 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. Λ S is determined from the difference between the μ - disappearance rate in hydrogen and the free muon decay rate. The result is based on the analysis of 1.2×1010 μ - decays, from which we extract the capture rate Λ S =(714.9±5. 4 stat ±5.1 syst ) s - 1 and derive the proton's pseudoscalar coupling g P (q02=-0.88mμ2)=8.06±0.55. © 2013 American Physical Society.