Multi-Lepton and Isolated Lepton Events at HERA

TL;DR

This paper reports on measurements of isolated high-energy leptons in ep collisions at HERA, comparing observed event yields with Standard Model predictions, and providing cross section measurements for multi-lepton and single W production events.

Contribution

It combines data from H1 and ZEUS to analyze multi-lepton and isolated lepton events, providing new cross section measurements and confirming Standard Model predictions.

Findings

Good agreement with Standard Model expectations

Observation of events with large transverse momentum

Measurement of total and differential cross sections

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.