Evidence for parity violation in neutral current induced π0 production from a comparison of neutrino and antineutrino cross sections

Abstract

Muonless single neutral pion production, by muon-neutrinos and antineutrinos, has been observed in a multiplate aluminum spark chamber. In order to test parity conservation the observed production rate by neutrinos has been compared with that by antineutrinos, scaled up with the well-known ratio of ν μ to ν μ -fluxes. These rates differ by a factor of 2, their difference being 4.3 standard deviations away from zero. This is strong evidence against a parity conserving semileptonic neutral current, e.g. pure vector or axial vector theories.