Search for gluino-mediated stop pair production in events with b-jets and large missing transverse momentum

A search for supersymmetry involving the pair production of gluions decaying via stop quarks into the lightest neutralino $\tilde{\chi}_{1}^{0}$ is reported. It uses LHC proton-proton collision data at the center-of-mass energy $\sqrt{s}=13 TeV$ with an integrated luminosity of $139 fb^{-1}$ collected with the ATLAS detector in 2015-2018. 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. The analysis is done in two final states, one of which is required to have at least 1 lepton, and the second one is required the veto on leptons. Expected exclusion limit for gluino and neutralino masses is evaluated using simplified signal model. It is found to be $800 GeV$ and below for neutralino masses with gluino masses of less than $2275 GeV$ at the $95\%$ confidence level.