PEN experiment: a precise measurement of the {pi}{sup +}{yields}e{sup +}{nu} decay branching fraction

A new measurement of B{sub {pi}}{sub e2}, the {pi}{sup +}{yields}e{sup +}{nu}({gamma}) decay branching ratio, is currently under way at the Paul Scherrer Institute. The present experimental result on B{sub {pi}}{sub e2} constitutes the most accurate test of lepton universality available. The accuracy, however, still lags behind the theoretical precision by over an order of magnitude. Because of the large helicity suppression of the {pi}{sub e2} decay, its branching ratio is susceptible to significant contributions from new physics, making this decay a particularly suitable subject of study.