Search for Higgs boson exotic decays into Lorentz-boosted light bosons in the four-τ final state at $\sqrt{s}$ = 13 with the ATLAS detector
A search for exotic decays of the Higgs boson into a pair of low-mass scalars that subsequently decay into τ-leptons, H → aa → τ + τ – τ + τ – , is presented. In models with Yukawa-like couplings, the decay to τ-leptons is favoured for light a-bosons, with mass in the range of 2m τ < m a < 2m b . Results are presented in the range of 4 GeV < m a < 15 GeV using the 140 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-τ pairs, one of the τ-leptons decays to hadrons and neutrinos, while the other decays to a muon and neutrinos. In this mass range, the a → τ + τ – is Lorentz-boosted and a dedicated muon removal technique is used to reconstruct the di-τ pairs.