The muon capture rate on hydrogen and the values of $g_A$ and $g_{\pi NN}$

Abstract

Motivated by the recent developments in the determination of the experimental values of the nucleon axial-vector coupling constant $g_A$ and the pion-nucleon coupling constant $g_{\pi NN}$, we carry out a heavy-baryon chiral perturbation calculation of the hyperfine-singlet $\mu p$ capture rate $\Gamma_0$ to next-to-next-to-leading order (N$^2$LO), with the use of the latest values of $g_A$ and $g_{\pi NN}$. The calculated N$^2$LO value is $\Gamma_0^{\rm theor}(\mu^- p \to \nu_\mu n) =718 \pm 7 \,s^{-1}$, where the estimated N$^3$LO contribution dominates the error. This value is in excellent agreement with the experimental value reported by the MuCap Collaboration.