Isolated tau leptons in events with large missing transverse momentum at HERA

TL;DR

This paper reports a search for isolated tau leptons with large missing transverse momentum at HERA, finding a few candidate events with results consistent with Standard Model expectations.

Contribution

First search for isolated tau leptons with large missing momentum at HERA, employing jet structure observables to distinguish tau decays from quark or gluon jets.

Findings

Three tau candidates observed versus 0.40 expected from SM.

Two high transverse momentum tau candidates found versus 0.20 expected.

Results are consistent with Standard Model predictions.

Abstract

A search for events containing isolated tau leptons and large missing transverse momentum, not originating from the tau decay, has been performed with the ZEUS detector at the electron-proton collider HERA, using 130 pb^-1 of integrated luminosity. A search was made for isolated tracks coming from hadronic tau decays. Observables based on the internal jet structure were exploited to discriminate between tau decays and quark- or gluon-induced jets. Three tau candidates were found, while 0.40 +0.12 -0.13 were expected from Standard Model processes, such as charged current deep inelastic scattering and single W-boson production. To search for heavy-particle decays, a more restrictive selection was applied to isolate tau leptons produced together with a hadronic final state with high transverse momentum. Two candidate events survive, while 0.20 +-0.05 events are expected from Standard Model processes.