Multi-Lepton Production at High Transverse Momenta in ep Collisions at   HERA
  Processes leading to a final state with at least two high transverse momentum leptons (electrons or muons) are studied using the full ep data sample collected by the H1 experiment at HERA. The data correspond to an integrated luminosity of 463 pb-1. Di-lepton and tri-lepton event classes are investigated. Cross sections of the production of e+e- and mu+mu- pairs are derived in a restricted phase space dominated by photon-photon collisions. In general, good agreement is found with Standard Model predictions. Events are observed with a total scalar sum of lepton transverse momenta above 100 GeV where the Standard Model expectation is low. In this region, combining di-lepton and tri-lepton classes, five events are observed in e+p collisions, compared to a Standard Model expectation of 0.96+-0.12, while no such event is observed in e-p data for 0.64+-0.09 expected. 
H1 Collaboration