Striking events with isolated charged leptons, large missing transverse momentum and large transverse momentum of the hadronic final state [Formula: see text] were observed at the electron proton collider HERA in a data sample corresponding to an integrated luminosity of about 130 pb-1. The H1 collaboration observed 11 events with isolated electrons or muons and with [Formula: see text]. Only 3.4±0.6 events were expected from Standard Model (SM) processes. Six of these events have [Formula: see text], while 1.3±0.3 events were expected. The ZEUS collaboration observed good agreement with the SM. However, ZEUS found two events with a similar event topology, but tau leptons instead of electrons or muons in the final state. Only 0.2±0.05 events were expected from SM processes. For various hypotheses, the compatibility of the experimental results was investigated with respect to the SM and with respect to possible explanations beyond the SM. Prospects for the high-luminosity HERA-II data taking period are given.
Two nucleon (B − L)-conserving reactions involving tau leptons