Observation of anomalous muon-electron pairs in a neutrino exposure

Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERNPS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π0 production, with one decay gamma lost. It was determined empirically, together with the small contribution from upsilonsub(e) reactions. For electron energies above 2GeV the background is 5.7 +- 1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10-4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axiom interactions. (orig.)