Di-Lepton Events In Bebc Narrow-Band Beam Neutrino Experiment

In film taken with BEBC filled with a Ne(74%mol)/H2 mixture and exposed to the CERN narrow-band neutrino beam (200 GeV), tenμ−μ+, one μ−μ+μ−and five μ−e+ events were found in the ν exposure and two μ+μ− events and one μ+e− event in the ν exposure. Assuming the same production mechanism for μμ and μe events, the relative rates, corrected for identification inefficiency and background, can be combined and are (1.3 ± 0.4)% for (μ−e+ + μ−μ+)/μ− in neutrino interactions, and (1.2 ± 0.5)% for (μ+e− + μ+μ−)/μ+ antineutrino interactions. Eight out of the sixteen μ−ℓ+ events have a V0, leading to a corrected K0-multiplicity of 1.7 ± 0.7. No evidence is found for heavy-lepton production.