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 e ± p 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 μ + μ - 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. © 2008 Elsevier B.V. All rights reserved.