Improved reconstruction of highly boosted tau-lepton pairs in the tau tau -> (mu nu _mu nu _tau)(hadrons + nu _tau) decay channels with the ATLAS detector

This paper presents a new tau-lepton reconstruction and identification procedure at the ATLASdetector at the Large Hadron Collider, which leads to significantly improved performance in the case of physics processes where a highly boosted pair of tau-leptons is produced and one tau-lepton decays into a muon and two neutrinos (tau_mu), and the other decays into hadrons and one neutrino (tau_had). By removing the muon information from the signals used for reconstruction and identification of the tau_had candidate in the boosted pair, the efficiency is raised to the level expected for an isolated tau_had. The new procedure is validated by selecting a sample of highly boosted Z -> tau_mu tau_had 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 -> tau_mu tau_had signal region and in a background validation region. The results presented in this paper demonstrate the effectiveness of the tau_had reconstruction with muon removal in enhancing the signal sensitivity of the boosted tau_mu tau_had channel at the ATLAS detector.