Multi-Lepton Production at High Transverse Momenta in ep Collisions at HERA

TL;DR

This paper analyzes high transverse momentum multi-lepton events in ep collisions at HERA, comparing observed data with Standard Model predictions, and reports an excess of events at high momentum sums in e+p collisions.

Contribution

It provides a comprehensive measurement of multi-lepton production at high transverse momenta using the full HERA data set, including observations of rare events.

Findings

Good agreement with Standard Model in most regions

Observation of 5 high-momentum events in e+p collisions where 0.96 expected

No such events observed in e-p collisions where 0.64 expected

Abstract

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.