Radiative Muon Capture on Hydrogen and the Induced Pseudoscalar Coupling

Abstract

The first measurement of the elementary process $\hat{I}{¼}^{-}p\to \hat{I}{½}_{\hat{I}}¼n{\hat{I}}^3$ is reported. A photon pair spectrometer was used to measure the partial branching ratio ($2.10\pm 0.22)\times 10^{-8}$ for photons of k > 60 MeV. The value of the weak pseudoscalar coupling constant determined from the partial branching ratio is $g_p(q^2=-0.88m_{\hat{I}}{¼}^2)=(9.8\pm 0.7\pm 0.3)\cdot g_a(0)$, where the first error is the quadrature sum of statistical and systematic uncertainties and the second error is due to the uncertainty in $\hat{I}{»}_{op}$, the decay rate of the ortho to para $p\hat{I}¼p$ molecule. This value of g_p is $\sim$1.5 times the prediction of PCAC and pion-pole dominance.

13 pages, RevTeX type, 3 figures (encapsulated postscript), submitted to Phys. Rev. Lett