Precise Determination of the Pion-Nuclear Coupling Parameter from Weak Processes in3He

We utilize precise weak interaction experiments on atomic muon capture and beta decay in the $A=3\mathrm{}$ nuclei and take into account the effects of nuclear “anomalous thresholds” to extract the pseudoscalar π${-}^3$He${-}^3$H coupling parameter, $G^{\mathrm{eff}}\left(m_{\pi }^2\right)=45.8\mathrm{}\pm 2.4$. This is an order of magnitude improvement in precision over that from the use of pion-nuclear scattering data and dispersion relations.