Improved reconstruction of highly boosted τ-lepton pairs in the ττ→(μνμ​ντ​)(hadrons+ντ​) decay channels with the ATLAS detector

This paper presents a new τ-lepton reconstruction and identification procedure at the ATLAS detector at the Large Hadron Collider, which leads to significantly improved performance in the case of physics processes where a highly boosted pair of τ-leptons is produced and one τ-lepton decays into a muon and two neutrinos (τμ​), and the other decays into hadrons and one neutrino (τhad​). By removing the muon information from the signals used for reconstruction and identification of the τhad​ candidate in the boosted pair, the efficiency is raised to the level expected for an isolated τhad​. The new procedure is validated by selecting a sample of highly boosted Z→τμ​τhad​ candidates from the data sample of 140 fb-1 of proton–proton collisions at 13 TeV recorded with the ATLAS detector. Good agreement is found between data and simulation predictions in both the Z→τμ​τhad​ signal region and in a background validation region. The results presented in this paper demonstrate the effectiveness of the τhad​ reconstruction with muon removal in enhancing the signal sensitivity of the boosted τμ​τhad​ channel at the ATLAS detector.