Journal Article

Estimation of backgrounds from jets misidentified as τ-leptons using the Universal Fake Factor method with the ATLAS detector

Ferrari, Arnaud, Zwalinski, L., Rincke, P., Ellert, Mattias, Gonzalez Suarez, Rebeca, Gallén, Axel, Ellajosyula, Venugopal, Aad, G., Mullier, Geoffrey A., Bergeås Kuutmann, Elin, Sunneborn Gudnadottir, Olga, Ekelöf, Tord, Brenner, Richard, Ripellino, Giulia

2025

Overview

Processes with tau-leptons in the final state are important for Standard Model measurements and searches for physics beyond the Standard Model. The ATLAS experiment at the Large Hadron Collider observes tau-leptons produced in proton-proton collisions only through their decay products. Data analyses involving hadronically decaying tau-leptons face challenges due to backgrounds from jets misidentified as tau-leptons that are not modelled reliably by Monte Carlo simulations. Data-driven methods such as the fake-factor method allow such misidentified backgrounds to be predicted by measuring transfer factors, known as fake factors, in data from dedicated regions. This paper describes a refined technique for determining the fake factors, the Universal Fake Factor method. It evaluates the fake factors for a signal region by using fake factors from samples enriched in different sources of jets misidentified as tau-leptons (light-quark, gluon, b-quark, and pile-up jets). Each fake factor is calculated as a linear combination of fake factors measured in these different enriched samples. For the full Run 2 data set, the systematic uncertainty of the calculated fake factors, evaluated using W(mu nu) enriched event sample, ranges from 15 to 35% depending on the tau-lepton's transverse momentum and charged-particle decay multiplicity.