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

Abstract

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 ${\Lambda }_S=725.0\pm 17.4s^{-1}$, from which the induced pseudoscalar coupling of the nucleon, $g_P(q^2=-0.88m_{\mu }^2)=7.3\pm 1.1$, is extracted. This result is consistent with theoretical predictions for $g_P$ that are based on the approximate chiral symmetry of QCD.

submitted to Phys.Rev.Lett

References in corpus (2)

• Improved Measurement of the Positive Muon Lifetime and Determination of the Fermi Constant
• Electroweak Radiative Corrections to Muon Capture

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