Search for long-lived charginos based on a disappearing-track signature using 136 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

TL;DR

This paper reports a search for long-lived charginos with disappearing tracks in proton-proton collisions at 13 TeV, setting new exclusion limits on chargino and gluino masses based on 136 fb$^{-1}$ of data.

Contribution

It introduces a novel search method for long-lived charginos using disappearing track signatures in ATLAS data, extending previous mass exclusion limits.

Findings

Chargino masses up to 660 GeV excluded for pure wino scenario.

Gluinos below 2.1 TeV excluded for certain chargino masses and lifetimes.

No significant excess observed above background expectations.

Abstract

A search for long-lived charginos produced either directly or in the cascade decay of heavy prompt gluino states is presented. The search is based on proton-proton collision data collected at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 136 fb$^{-1}$. Long-lived charginos are characterised by a distinct signature of a short and then disappearing track, and are reconstructed using at least four measurements in the ATLAS pixel detector, with no subsequent measurements in the silicon-microstrip tracking volume nor any associated energy deposits in the calorimeter. The final state is complemented by a large missing transverse-momentum requirement for triggering purposes and at least one high-transverse-momentum jet. No excess above the expected backgrounds is observed. Exclusion limits are set at 95% confidence level on the masses of the chargino and gluino for different chargino lifetimes. Chargino masses up to 660 (210) GeV are excluded in scenarios where the chargino is a pure wino (higgsino). For charginos produced during the cascade decay of a heavy gluino, gluinos with masses below 2.1 TeV are excluded for a chargino mass of 300 GeV and a lifetime of 0.2 ns.