New results in rare allowed muon and pion decays

D. Pocanic; E. Munyangabe; M. Bychkov; V. A. Baranov; W. Bertl; Yu. M. Bystritsky; E. Frlez; V. A. Kalinnikov; N. V. Khomutov; A. S. Korenchenko; S. M. Korenchenko; M. Korolija; T. Kozlowski; N. P. Kravchuk; N. A. Kuchinsky; M. C. Lehman; D. Mekterovic; D. Mzhavia; A. Palladino; P. Robmann; A. M. Rozhdestvensky; I. Supek; P. Truoel; Z. Tsamalaidze; A. van der Schaaf; B. Vandevender; E. P. Velicheva; V. P. Volnykh

doi:10.1142/s2010194514604372

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arXiv · 1403.7416

New results in rare allowed muon and pion decays

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Abstract

Simple dynamics, few available decay channels, and highly controlled radiative and loop corrections, make pion and muon decays a sensitive means of exploring details of the underlying symmetries. We review the current status of the rare decays: pi+ -> e+ nu, pi+ -> e+ nu gamma, pi+ -> pi0 e+ nu, and mu+ -> e+ nu nu-bar gamma. For the latter we report new preliminary values for the branching ratio B(E_gamma >10 MeV, theta_(e-gamma) > 30deg) = 4.365 (9)_stat (42)_syst x 10^{-3}, and the decay parameter eta-bar = 0.006 (17)_stat (18)_syst, both in excellent agreement with standard model predictions. We review recent measurements, particularly by the PIBETA and PEN experiments, and near-term prospects for improvement. These and other similar precise low energy studies complement modern collider results materially.

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D. Pocanic, E. Munyangabe, M. Bychkov, V. A. Baranov, W. Bertl, Yu. M. Bystritsky, E. Frlez, V. A. Kalinnikov, N. V. Khomutov, A. S. Korenchenko, S. M. Korenchenko, M. Korolija, T. Kozlowski, N. P. Kravchuk, N. A. Kuchinsky, M. C. Lehman, D. Mekterovic, D. Mzhavia, A. Palladino, P. Robmann, A. M. Rozhdestvensky, I. Supek, P. Truoel, Z. Tsamalaidze, A. van der Schaaf, B. Vandevender, E. P. Velicheva, V. P. Volnykh. 2014-03-28. New results in rare allowed muon and pion decays. https://doi.org/10.1142/s2010194514604372

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