Reconstruction and identification of boosted di-$\tau$ systems in a search for Higgs boson pairs using 13 TeV proton$-$proton collision data in ATLAS

TL;DR

This paper introduces a new di-$\tau$ tagger technique for identifying boosted tau pairs in proton-proton collision data, applied in a search for Higgs boson pairs, resulting in no observed deviations and setting exclusion limits.

Contribution

A novel di-$\tau$ tagging method was developed and applied in the ATLAS experiment for the first time to improve Higgs pair searches at 13 TeV.

Findings

Di-$\tau$ tagger efficiency was measured.

Background from misidentified jets was estimated.

No significant excess found, limits set on heavy scalar resonances.

Abstract

In this paper, a new technique for reconstructing and identifying hadronically decaying $\tau^+\tau^-$ pairs with a large Lorentz boost, referred to as the di-$\tau$ tagger, is developed and used for the first time in the ATLAS experiment at the Large Hadron Collider. A benchmark di-$\tau$ tagging selection is employed in the search for resonant Higgs boson pair production, where one Higgs boson decays into a boosted $b\bar{b}$ pair and the other into a boosted $\tau^+\tau^-$ pair, with two hadronically decaying $\tau$-leptons in the final state. Using 139 fb$^{-1}$ of proton$-$proton collision data recorded at a centre-of-mass energy of 13 TeV, the efficiency of the di-$\tau$ tagger is determined and the background with quark- or gluon-initiated jets misidentified as di-$\tau$ objects is estimated. The search for a heavy, narrow, scalar resonance produced via gluon$-$gluon fusion and decaying into two Higgs bosons is carried out in the mass range 1$-$3 TeV using the same dataset. No deviations from the Standard Model predictions are observed, and 95% confidence-level exclusion limits are set on this model.