Search for a light CP-odd Higgs boson decaying into a pair of $\tau$-leptons in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract

This paper reports a search for a light CP-odd scalar resonance with a mass of 20 GeV to 90 GeV in 13 TeV proton-proton collision data with an integrated luminosity of 140 fb${}^{-1}$ collected with the ATLAS detector at the Large Hadron Collider. The analysis assumes the resonance is produced via gluon-gluon fusion and decays into a ${\tau }^{+}{\tau }^{-}$ pair which subsequently decays into a fully leptonic ${\mu }^{+}{\nu }_{\mu }{\bar{\nu }}_{\tau }{e}^{-}{\bar{\nu }}_e{\nu }_{\tau }$ or $e^{+}{\nu }_e{\bar{\nu }}_{\tau }{\mu }^{-}{\bar{\nu }}_{\mu }{\nu }_{\tau }$ final state. No significant excess of events above the predicted Standard Model background is observed. The results are interpreted within a flavour-aligned two-Higgs-doublet model, and a model-independent cross-section interpretation is also given. Upper limits at 95 confidence level between 3.0 pb and 68 pb are set on the cross-section for producing a CP-odd Higgs boson that decays into a ${\tau }^{+}{\tau }^{-}$ pair.

52 pages in total, author list starting page 35, 8 figures, 5 tables, published by JHEP. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HDBS-2021-08/

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