A data-driven multijet background estimation method for the search for direct pair production of scalar tau leptons with the ATLAS detector

As a proposed fundamental symmetry of nature, Supersymmetry provides elegant solutions to various open questions of the Standard Model by predicting superpartners of known particles, whose spins differ by one half unit. In R-parity-conserving models, these hypothetical particles are produced in pairs and decay ultimately into the stable, lightest supersymmetric particle, a candidate for dark matter. A search for direct production of scalar tau leptons in final states with two hadronically decaying tau leptons and missing transverse momentum is presented. The simplified signal models consider scalar tau leptons decaying exclusively into a tau lepton and a stable neutralino. Such a production mode may dominate if the strongly interacting superpartners and gauginos are heavy and thus beyond the reach of currently probed energy scales. The analysis uses pp collision data at a center-of-mass energy of 13 TeV, recorded with the ATLAS detector from 2015 to 2018. The background for the investigated signature is dominated by multijet production via the strong interaction, where jets fake the detector signature of a hadronically decaying tau lepton. For the estimation of this background a data-driven fake-factor method is presented.