Observation of Events with an Isolated High Energy Lepton and Missing Transverse Momentum at HERA

TL;DR

This paper reports the observation of events with isolated high-energy leptons and missing transverse momentum at HERA, some consistent with W boson production and others exhibiting atypical kinematic properties.

Contribution

It presents the first observation of such events at HERA, highlighting potential deviations from Standard Model expectations.

Findings

Six events with isolated high-energy leptons and missing transverse momentum were observed.

Three events are consistent with W boson production, while three show atypical kinematic features.

Evidence suggests possible new physics or unaccounted Standard Model processes.

Abstract

A search for events with an imbalance in transverse momentum and with isolated high energy leptons has been carried out at the positron-proton collider HERA. One event with an e^- and five events with a mu^+- are found together with evidence for undetected particles carrying transverse momentum. Within the Standard Model the dominant origin of events with this kind of topology is the production of W bosons with subsequent leptonic decay. Three of the six events are within measurement errors found in a region of phase space likely to be populated by this process, while the remaining events show kinematic properties which are atypical of all Standard Model processes considered.