Search for phenomena beyond the Standard Model in events with large b-jet multiplicity using the ATLAS detector at the LHC

Abstract

Events with a large number of high-$p_{\text{T}}$ $b$-jets are rare in the Standard Model (SM); an excess of events with such topology would be a signal of phenomena beyond the SM. One phenomenon where a large excess is expected is a variant of Supersymmetry in which R-parity is violated, allowing baryon number violating decays of the super partners of the SM particles. This document presents the search for physics beyond the SM in events with at least eight jets and at least six $b$-jets. It was performed using Run 2 data collected by the ATLAS detector corresponding to an integrated luminosity of 139 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV. We consider specifically the production of a pair of heavy top squarks which decay to a $b$-quark and a chargino, which in turn decays into $bbs$ via a virtual top squark. The most dominant source of background is multijet production, estimated using a data-driven technique. A fit is performed to estimate the expected sensitivity of the signal strength. Expected and observed 95$\%$ CL upper limits are set based on the top squark and chargino masses.