Improved reconstruction of highly boosted τ-lepton pairs in the ττ→(μνμντ)(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→τμτhad 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→τμτhad 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 τμτhad channel at the ATLAS detector.