Search for supersymmetry in final states with missing transverse momentum and three or more $b$-jets in 139 fb$^{-1}$ of proton$-$proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

TL;DR

This paper reports a search for supersymmetry involving gluino pair production with specific decay modes, using extensive LHC data, and sets new exclusion limits on gluino masses with no significant signal observed.

Contribution

It introduces a search strategy combining simple kinematic cuts and deep neural networks to improve sensitivity in supersymmetry searches at the LHC.

Findings

No significant excess found over background predictions.

Gluino masses below 2.44 TeV are excluded for certain decay models.

Limits are set on gluino masses in various decay scenarios.

Abstract

A search for supersymmetry involving the pair production of gluinos decaying via off-shell third-generation squarks into the lightest neutralino ($\tilde\chi^0_1$) is reported. It exploits LHC proton$-$proton collision data at a centre-of-mass energy $\sqrt{s} = 13$ TeV with an integrated luminosity of 139 fb$^{-1}$ collected with the ATLAS detector from 2015 to 2018. The search uses events containing large missing transverse momentum, up to one electron or muon, and several energetic jets, at least three of which must be identified as containing $b$-hadrons. Both a simple kinematic event selection and an event selection based upon a deep neural-network are used. No significant excess above the predicted background is found. In simplified models involving the pair production of gluinos that decay via off-shell top (bottom) squarks, gluino masses less than 2.44 TeV (2.35 TeV) are excluded at 95% CL for a massless $\tilde\chi^0_1$. Limits are also set on the gluino mass in models with variable branching ratios for gluino decays to $b\bar{b}\tilde\chi^0_1$, $t\bar{t}\tilde\chi^0_1$ and $t\bar{b}\tilde\chi^-_1$ / $\bar{t}b\tilde\chi^+_1$.