Ortho-para transition rate in $\hat{I}¼$-molecular hydrogen and the proton's induced pseudoscalar coupling $g_p$

Abstract

We report a measurement of the ortho-para transition rate in the p$\hat{I}¼$p molecule. The experiment was conducted at TRIUMF via the measurement of the time dependence of the 5.2 MeV neutrons from muon capture in liquid hydrogen. The measurement yielded an ortho-para rate $\hat{I}{›}_{op}=(11.1\pm 1.7{\pm }_{0.6}^{0.9})\times 10^4$ s${}^{-1}$ that is substantially larger than the earlier result of Bardin {\it et al.} We discuss the striking implications for the proton's induced pseudoscalar coupling $g_p$.

4 pages, 3 figures, submitted to Phys. Rev. Lett