A search for the decays of stopped long-lived particles at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This paper reports a search for long-lived particles that stop within the ATLAS detector and decay, producing high-energy jets, with the analysis setting new limits on gluino R-hadron masses at 13 TeV.

Contribution

It introduces a novel search method for stopped long-lived particles using out-of-time calorimeter energy deposits in ATLAS data from 2017-2018.

Findings

Excluded gluino R-hadron masses up to 1.4 TeV for certain lifetimes.

Set lower limits on gluino R-hadron masses assuming specific decay branching fractions.

Analyzed 579 hours of data during LHC non-collision periods.

Abstract

A search for long-lived particles, which have come to rest within the ATLAS detector, is presented. The subsequent decays of these long-lived particles can produce high-momentum jets, resulting in large out-of-time energy deposits in the ATLAS calorimeters. These decays are detected using data collected during periods in the LHC bunch structure when collisions are absent. The analysed dataset is composed of events from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s}=13$ TeV and recorded by the ATLAS experiment during 2017 and 2018. The dataset used for this search corresponds to a total live time of 579 hours. The results of this search are used to derive lower limits on the mass of gluino $R$-hadrons, assuming a branching fraction $B(\tilde{g} \rightarrow q \bar{q} \tilde{\chi}_1^0)=100$%, with masses of up to 1.4 TeV excluded for gluino lifetimes of $10^{-5}$ to $10^3$ s.