Search for Higgs boson decays into a pair of pseudoscalar particles in the γγτhadτhad final state using pp collisions at √s = 13 TeV with the ATLAS detector

Abstract

A search for exotic decays of the 125 GeV Higgs boson into a pair of new spin-0particles, H → aa, where one decays into a photon pair and the other into a τ -lepton pair,is presented. Hadronic decays of the τ -leptons are considered and reconstructed using adedicated tagger for collimated τ -lepton pairs. The search uses 140 fb−1 of proton-protoncollision data at a centre-of-mass energy of √s = 13TeV recorded between 2015 and 2018 bythe ATLAS experiment at the Large Hadron Collider. The search is performed in the massrange of the a boson between 10 GeV and 60 GeV. No significant excess of events is observedabove the Standard Model background expectation. Model-independent upper limits at 95%confidence level are set on the branching ratio of the Higgs boson to the γγτ τ final state,B(H → aa → γγτ τ ), ranging from 0.2% to 2%, depending on the a-boson mass hypothesis.