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

Abstract

This paper presents a new $\tau$-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 $\tau$-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 $Z\to {\tau }_{\mu }{\tau }_{had}$ 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 $Z\to {\tau }_{\mu }{\tau }_{had}$ 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.

arXiv comment44 pages in total, author list starting page 27, 13 figures, 2 tables. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TAUP-2023-02

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