Search for long-lived, massive particles in events with displaced vertices and multiple jets in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

TL;DR

This paper reports a search for long-lived particles decaying into hadrons using ATLAS data, employing specialized techniques to improve detection sensitivity, and sets new limits on supersymmetric particle models with long lifetimes.

Contribution

It introduces advanced reconstruction methods for detecting long-lived particles and provides the first constraints on certain supersymmetric scenarios with long-lived electroweakinos.

Findings

Electroweakinos with masses below 1.5 TeV are excluded for lifetimes 0.03-1 ns.

Electroweakinos from 2.4 TeV gluino decays are excluded for lifetimes 0.02-4 ns.

No significant excess over background was observed.

Abstract

A search for long-lived particles decaying into hadrons is presented. The analysis uses 139 fb$^{-1}$ of $pp$ collision data collected at $\sqrt{s} = 13$ TeV by the ATLAS detector at the LHC using events that contain multiple energetic jets and a displaced vertex. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particles decaying in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are used to set limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and on scenarios with pair-production of supersymmetric particles with long-lived electroweakinos that decay via a small $R$-parity-violating coupling. The pair-production of electroweakinos with masses below 1.5 TeV is excluded for mean proper lifetimes in the range from 0.03 ns to 1 ns. When produced in the decay of $m(\tilde{g})=2.4$ TeV gluinos, electroweakinos with $m(\tilde\chi^0_1)=1.5$ TeV are excluded with lifetimes in the range of 0.02 ns to 4 ns.