New studies of allowed pion and muon decays

• Published in: arXiv.org
• Main Authors: Pocanic, D, Palladino, A, Alonzi, L P, Baranov, V A, Bertl, W, Bychkov, M, Bystritsky, Yu M, Frlez, E, Kalinnikov, V A, Khomutov, N V, Korenchenko, A S, Korenchenko, S M, Korolija, M, Kozlowski, T, Kravchuk, N P, Kuchinsky, N A, Lehman, M C, Mekterovic, D, Munyangabe, E, Mzhavia, D, Robmann, P, Rozhdestvensky, A M, Shkarovskiy, S N, Straumann, U, Supek, I, Truöl, P, Tsamalaidze, Z, van der Schaaf, A, Velicheva, E P, Volnykh, V P
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 18.10.2012
• Subjects: Decay; Helicity; Leptons; Muons; Physics - High Energy Physics - Experiment; Physics - Nuclear Experiment
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1210.5025

Building on the rare pion and muon decay results of the PIBETA experiment, the PEN collaboration has undertaken a precise measurement of B_{\pi e2} = R^\pi_{e/\mu}, the \pi^+ -> e^+\nu(\gamma) decay branching ratio, at the Paul Scherrer Institute, to reduce the present 40\times experimental precision lag behind theory to ~ 6-7\times. Because of large helicity suppression, R^\pi_{e/\mu} is uniquely sensitive to contributions from non-(V-A) physics, making this decay a particularly suitable subject of study. Even at current precision, the experimental value of B_{\pi e2} provides the most accurate test of lepton universality available. During runs in 2008-10, PEN has accumulated over 2\times 10^7 \pi_{e2} events; a comprehensive maximum-likelihood analysis is currently under way. The new data will also lead to improved precision of the earlier PIBETA results on radiative \pi and \mu decays.