Measurement of Muon Capture on the Proton to 1% Precision and Determination of the Pseudoscalar Coupling g_P

TL;DR

The MuCap experiment precisely measured muon capture on hydrogen, determining the capture rate and the proton's pseudoscalar coupling g_P with 1% accuracy, providing critical tests of weak interaction theories.

Contribution

This work provides the most precise measurement of muon capture rate on hydrogen and accurately determines the pseudoscalar coupling g_P, improving upon previous experimental uncertainties.

Findings

Capture rate L_S = (714.9 +- 5.4(stat) +- 5.1(syst)) s^-1

Pseudoscalar coupling g_P(q^2_0 = -0.88 m^2_mu) = 8.06 +- 0.55

Supports theoretical predictions of weak interactions in nucleons

Abstract

The MuCap experiment at the Paul Scherrer Institute has measured the rate L_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, ultra-pure hydrogen gas. Cylindrical wire chambers and a segmented scintillator barrel detected electrons from muon decay. L_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 10^10 mu- decays, from which we extract the capture rate L_S = (714.9 +- 5.4(stat) +- 5.1(syst)) s^-1 and derive the proton's pseudoscalar coupling g_P(q^2_0 = -0.88 m^2_mu) = 8.06 +- 0.55.