Measurement of the Rate of Muon Capture in Hydrogen Gas and Determination of the Proton's Pseudoscalar Coupling $g_P

• Main Authors: Andreev, V. A, Banks, T. I, Case, T. A, Chitwood, D. B, Clayton, S. M, Crowe, K. M, Deutsch, J, Egger, J, Freedman, S. J, Ganzha, V. A, Gorringe, T, Gray, F. E, Hertzog, D. W, Hildebrandt, M, Kammel, P, Kiburg, B, Knaack, S, Kravtsov, P. A, Krivshich, A. G, Lauss, B, Lynch, K. L, Maev, E. M, Maev, O. E, Mulhauser, F, Özben, C. S, Petitjean, C, Petrov, G. E, Prieels, R, Schapkin, G. N, Semenchuk, G. G, Soroka, M. A, Tishchenko, V, Vasilyev, A. A, Vorobyov, A. A, Vznuzdaev, M. E, Winter, P
• Format: Journal Article
• Language: English
• Published: 16.04.2007
• Subjects: Physics - Nuclear Experiment
• DOI: 10.48550/arxiv.0704.2072

Phys.Rev.Lett.99:032002,2007 The rate of nuclear muon capture by the proton has been measured using a new experimental technique based on a time projection chamber operating in ultra-clean, deuterium-depleted hydrogen gas at 1 MPa pressure. The capture rate was obtained from the difference between the measured $\mu^-$ disappearance rate in hydrogen and the world average for the $\mu^+$ decay rate. The target's low gas density of 1% compared to liquid hydrogen is key to avoiding uncertainties that arise from the formation of muonic molecules. The capture rate from the hyperfine singlet ground state of the $\mu p$ atom is measured to be $\Lambda_S=725.0 \pm 17.4 s^{-1}$, from which the induced pseudoscalar coupling of the nucleon, $g_P(q^2=-0.88 m_\mu^2)=7.3 \pm 1.1$, is extracted. This result is consistent with theoretical predictions for $g_P$ that are based on the approximate chiral symmetry of QCD.