The pion beta and radiative electronic decays

Abstract

As the lightest meson, pion offers unique opportunities for measuring parameters and testing limits of the Standard Model (SM). The PiBeta experiment, carried out at PSI, focused on SM tests accessible through the pion beta, \pi^+ \to \pi^0e^+\nu_e(\gamma)π+→π0e+νe(γ), and electronic radiative, \pi^+ \to e^+\nu_e\gammaπ+→e+νeγ, decay channels. We review the PiBeta experiment, and update the pion beta decay branching ratio B^{\text{exp}}_{\pi\beta}=1.038(6)_{\text{tot}}\times10^{-8}Bπβexp=1.038(6)tot×10−8, along with the corresponding derived value of the Cabibbo-Kobayashi-Maskawa matrix element V_{ud} = 0.9738(28)Vud=0.9738(28).