New studies of allowed pion and muon decays
hep-ex
/ Authors
D. Pocanic, A. Palladino, L. P. Alonzi, V. A. Baranov, W. Bertl, M. Bychkov, Yu. M. Bystritsky, E. Frlez, V. A. Kalinnikov, N. V. Khomutov
and 20 more authors
A. S. Korenchenko, S. M. Korenchenko, M. Korolija, T. Kozlowski, N. P. Kravchuk, N. A. Kuchinsky, M. C. Lehman, D. Mekterovic, E. Munyangabe, D. Mzhavia, P. Robmann, A. M. Rozhdestvensky, S. N. Shkarovskiy, U. Straumann, I. Supek, P. Truöl, Z. Tsamalaidze, A. van der Schaaf, E. P. Velicheva, V. P. Volnykh
/ Abstract
Building on the rare pion and muon decay results of the PIBETA experiment, the PEN collaboration has undertaken a precise measurement of B_{πe2} = R^π_{e/μ}, the π^+ -> e^+ν(γ) 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^π_{e/μ} 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_{πe2} provides the most accurate test of lepton universality available. During runs in 2008-10, PEN has accumulated over 2\times 10^7 π_{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 πand μdecays.