Search for finite-mass neutrinos in the decay [formula omitted

Abstract

If neutrinos possess non-zero mass, pion decay might have small decay branches to neutrino states with large masses. We have searched for such branches in the decay of pions produced at the Indiana University Cyclotron. The energy spectrum of decay muons shows no evidence for such neutrino branches and if these decays do exist, their branching ratios must be less than 10 −2 to 10 −3 for neutrino masses in the ranFge 7–33 MeV.