Abstract
A new precision measurement of the branching ratio of the rare pion decay into a positron and a neutrino (π→eν) has been completed. A beam of positive pions was stopped in an active target of plastic scintillator surrounded by a 4π BGO calorimeter. 3× rare decays and 1.2× normal pion decays (π→μν) were recorded. The branching ratio was finally calculated from 1.2× rare decays after various cuts in the time window from 7.5 to 200 ns after pion stop. The errors of the result (1.235±0.005)× are 0.28% statistical and 0.29% systematical.
- Received 24 July 1992
DOI:https://doi.org/10.1103/PhysRevLett.70.17
©1993 American Physical Society