Improved reconstruction of highly boosted $\tau$-lepton pairs in the $\tau\tau\rightarrow(\mu\nu_{\mu}\nu_{\tau})({hadrons}+\nu_{\tau})$ decay channels with the ATLAS detector

The ATLAS collaboration
Aad, Georges , Aakvaag, Erlend , Abbott, Braden Keim , Abdelhameed, Sara , Abeling, Kira , Abicht, Nils Julius , Abidi, Haider , Aboelela, Mohammed , Aboulhorma, Asmaa , Abramowicz, Halina
Eur.Phys.J.C 85 (2025) 706, 2025.

Abstract (data abstract)
This paper presents a new $\tau$-lepton reconstruction and identification procedureat 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 $\tau$-leptons is produced and one $\tau$-lepton decaysinto 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 signalsused 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 $Z\rightarrow\tau_{\mu}\tau_{had}$ 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 $Z\rightarrow\tau_{\mu}\tau_{had}$ 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.

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