Search for 𝑅-parity violating supersymmetric decays of the top squark to a 𝑏-jet and a lepton in √𝑠 =13  TeV 𝑝⁢𝑝 collisions with the ATLAS detector

A search is presented for direct pair production of the stop, the supersymmetric partner of the top quark, in a decay through an 𝑅-parity violating coupling to a charged lepton and a 𝑏-quark. The dataset corresponds to an integrated luminosity of 140  fb−1 of proton-proton collisions at a center-of-mass energy of √𝑠 =13  TeV collected between 2015 and 2018 by the ATLAS detector at the LHC. The final state has two charged leptons (electrons or muons) and two 𝑏-jets. The results of the search are interpreted in the context of a Minimal Supersymmetric Standard Model with an additional 𝐵 −𝐿 gauge symmetry that is spontaneously broken. No significant excess is observed over the Standard Model background, and exclusion limits on stop pair production are set at 95% confidence level. The corresponding lower limits on the stop mass for 100% branching ratios to a 𝑏-quark and an electron, muon, or tau-lepton are 1.9 TeV, 1.8 TeV and 800 GeV, respectively, extending the reach of previous LHC searches.