Search for Higgs boson exotic decays into Lorentz-boosted light bosons in the four-$\tau$ final state at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract

A search for exotic decays of the Higgs boson into a pair of low-mass scalars that subsequently decay into $\tau$-leptons, $H\to aa\to {\tau }^{+}{\tau }^{-}{\tau }^{+}{\tau }^{-}$, is presented. In models with Yukawa-like couplings, the decay to $\tau$-leptons is favoured for light $a$-bosons, with mass in the range of $2m_{\tau }<m_a<2m_b$. Results are presented in the range of $4\mathrm{GeV}<m_a<15\mathrm{GeV}$ using the $140{\mathrm{fb}}^{-1}$ of proton-proton collisions at $\sqrt{s}=13$ TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider. This search focuses on the scenario where, for both di-$\tau$ pairs, one of the $\tau$-leptons decays to hadrons and neutrinos, while the other decays to a muon and neutrinos. In this mass range, the $a\to {\tau }^{+}{\tau }^{-}$ is Lorentz-boosted and a dedicated muon removal technique is used to reconstruct the di-$\tau$ pairs. No significant excess above the Standard Model background prediction is observed. Upper limits on $(\sigma (H)/{\sigma }_{\mathrm{SM}}(H))\times \mathcal{B}(H\to aa\to 4\tau )$ at $95\%$ confidence level are provided, ranging from $0.03$ to $0.10$ depending on the $a$-boson mass.

38 pages in total, author list starting page 21, 5 figures, 1 table, published in Phys. Lett. B. All figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HMBS-2024-25/

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