Reconstruction and identification of pairs of collimated τ -leptons decaying hadronically using √s = 13 TeV pp collision data with the ATLAS detector

Abstract

This paper describes an algorithm for reconstructingand identifying a highly collimated hadronicallydecaying τ -lepton pair with low transverse momentum.Whentwo τ -leptons are highly collimated, their visible decayproducts might overlap, degrading the reconstruction performancefor each of the τ -leptons. A dedicated treatmentattempting to tag the τ -lepton pair as a single object isrequired. The reconstruction algorithm is based on a largeradius jet and its associated two leading subjets, and the identificationuses a boosted decision tree to discriminate betweensignatures from τ+τ- systems and those arising from QCDjets. The efficiency of the identification algorithm is measSQUARE ROOTured in Zγ events using proton-proton collision data ats = 13 TeV collected by the ATLAS experiment at theLarge Hadron Collider between 2015 and 2018, correspondingto an integrated luminosity of 139 fb-1. The resultingdata-to-simulation scale factors are close to unity with uncertainties ranging from 26 to 37%.