Improved reconstruction of highly boosted τ-lepton pairs in the ττ → (μν_μν_τ) (hadrons + ν_τ) 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 (τ_μ), and the other decays into hadrons and one neutrino (τ_had). By removing the muon information from the signals used for reconstruction and identification of the τ_had candidate in the boosted pair, the efficiency is raised to the level expected for an isolated τ_had. The new procedure is validated by selecting a sample of highly boosted 𝑍 → τ_μτ_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 → τ_μτ_had signal region and in a background validation region. The results presented in this paper demonstrate the effectiveness of the τ_had reconstruction with muon removal in enhancing the signal sensitivity of the boosted τ_μτ_had channel at the ATLAS detector.