Multi-Lepton and Isolated Lepton Events at HERA

Abstract

Measurements of the production of events containing isolated high energy leptons (electrons and muons) produced in ep collisions have been performed with the H1 and ZEUS detectors at HERA, using data collected in the period 1994-2007. Topologies with more than one charged lepton or with a charged lepton in coincidence with missing transverse momentum are analysed. The H1 and ZEUS data, corresponding to an integrated luminosity of about 0.5 fb^-1 per experiment, are combined in a common phase space. The observed event yields are compared to the predictions from the Standard Model. In general a good agreement is found, where the expectation is dominated by photon-photon collisions for the multi-lepton topologies and by single W production in the case of events with an isolated electron or muon and missing transverse momentum. Events with large transverse momentum are observed. Total and differential cross sections of these processes are measured.