Observation of Prompt Neutrinos from 400-GeV Proton Nucleus Collisions

Abstract In 70 000 photos taken in BEBC during an experiment in which the 400 GeV proton beam of the CERN SPS was dumped into a massive Cu target 820 m upstream of BEBC, 70 interactions induced by neutral primaries above 10 GeV were observed. In 11 events the secondary charged lepton is an e − , in four events an e + . This number of electron events cannot be due to electron neutrinos from conventional sources (K, Λ, Σ − decays). The flux of the additional (prompt) neutrinos is evaluated. Possible origins are discussed in terms of charmed particles, τ's, and as yet undiscovered particles. Limits are given on axion production.