Mu Capture, Beta Decay, and Pi-Meson Decay

In the original Yukawa formulation of meson theory, π meson (as we now believe Yukawa's particle to ) was to provide a natural explanation for β decay. process π → e + ν[bar] was regarded as an elementary and nuclear β decay was imagined to proceed the route n → p + π → μ + e + ν[bar]. There are a variety reasons why this scheme fails. Just the opposite point view is now generally adopted, namely, that the β decay is fundamental and that the observed of the π meson is to be explained in terms of it. do not exclude the possibility that β decay be in terms of an as yet unknown heavy intermediate. , the nuclear β decay is to be as essentially primary. In order to describe the dominant π-meson decay mode π → μ + ν[bar] it is to assume the existence of another β decay process, μ-meson capture. The elementary process be described as μ + p → n + ν, or equally well as + p[bar] → μ + ν[bar]; the first is the experimentally observed μ-meson absorption reaction, whereas, the second, the of a neutron and an antiproton, plays an role in π-meson decay.