New studies of allowed pion and muon decays

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-e/mu(pi), the pi(vertical bar) -> e(vertical bar) nu(gamma) decay branching ratio, at the Paul Scherrer Institute, to reduce the present 40x experimental precision lag behind theory to similar to 6-7x. Because of large helicity suppression, R-e/mu(pi) 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 2x10(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.