Search for long-lived neutral particles decaying into lepton jets in proton--proton collisions at $\sqrt{s}$ = 8 TeV with the ATLAS detector

TL;DR

This paper reports a search for long-lived neutral particles decaying into collimated lepton jets in 8 TeV proton-proton collisions, setting limits on models with Higgs decays to such particles using ATLAS data.

Contribution

First search for long-lived neutral particles decaying into lepton jets at the LHC with detailed limits on Higgs decay models.

Findings

No significant excess observed.

Limits set on Higgs decay to long-lived lepton jets.

Constraints depend on the particle's proper decay length.

Abstract

Several models of physics beyond the Standard Model predict neutral particles that decay into final states consisting of collimated jets of light leptons and hadrons (so-called "lepton jets"). These particles can also be long-lived with decay length comparable to, or even larger than, the LHC detectors' linear dimensions. This paper presents the results of a search for lepton jets in proton--proton collisions at the centre-of-mass energy of $\sqrt{s}$ = 8 TeV in a sample of 20.3 fb$^{-1}$ collected during 2012 with the ATLAS detector at the LHC. Limits on models predicting Higgs boson decays to neutral long-lived lepton jets are derived as a function of the particle's proper decay length.