Estimates of Lepton Backgrounds for Slepton Searches in Compressed Mass Scenarios at the ATLAS Experiment

Supersymmetry (SUSY) is a highly motivated extension of the Standard Model (SM) that can solve many of the outstanding problems in the SM. A search for for selectrons ($widetilde{e}$) and smuons ($widetilde{mu}$) in models with compressed mass spectra is currently underway at the ATLAS collaboration at CERN. The model assumes $R$-parity conserving supersymmetry where the lightest supersymmetric partner (LSP) is a neutralino with a mass that is very close to that of the slepton. Specifically, the mass-splitting between the $widetilde{e}$ or $widetilde{mu}$ and the LSP is on the order of 20-70 GeV. The smuon search is particularly motivated, as it could provide a SUSY explanation to the muon $g-2$ anomaly.

This search utilizes soft leptons. The most challenging backgrounds for these leptons arise from hadrons mimicking the signature of prompt leptons, called `fake leptons,' and real leptons that did not come from the primary interacting in the event, called `non-prompt leptons.' These backgrounds are not well-modeled in simulation, and thus a data-driven method is used, called the Fake Factor (FF) Method. The background estimations for this search of the fake and non-prompt leptons using the FF Method are presented. This search uses 139 fb$^{-1}$ of $sqrt{s} = 13$ TeV $pp$ collision data collected between 2015 and 2018 by the ATLAS detector at the Large Hadron Collider.