Search for supersymmetry in final states with missing transverse momentum and multiple $b$-jets in proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino ($\displaystyle\tilde\chi^0_1$) is reported. It uses LHC proton-proton collision data at a centre-of-mass energy $\sqrt{s} = 13$ TeV with an integrated luminosity of 79.9 fb$^{-1}$ collected with the ATLAS detector from 2015 to 2017. The search is performed in events containing large missing transverse momentum and several energetic jets, at least three of which must be identified as originating from $b$-quarks. No excess is found above the predicted background. For $\displaystyle\tilde\chi^0_1$ masses below approximately 800 GeV, gluino masses of less than 2.23 TeV (2.19) TeV are excluded at 95 % confidence level in simplified models involving the pair production of gluinos that decay via top (bottom) squarks. An interpretation of the limits in terms of the branching ratios of the gluinos into third-generation squarks is also provided.