engAikot, AryaSearch for Higgs boson decays into a pair of pseudoscalar particles in the $\gamma\gamma\tau\tau$ final state using $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detectorParticle Physics - ExperimentATL-PHYS-SLIDE-2025-622Many well-motivated extensions of the Standard Model predict light (pseudo)scalars, referred to as 𝑎 bosons, that couple to the 125 GeV Higgs boson, enabling new exotic decay modes. This study presents a search for Higgs boson decays into a pair of such particles, $H\rightarrow bb$, where one 𝑎-boson decays into a photon pair and the other into a $\tau$-lepton pair, performed for the first time at the Large Hadron Collider. Both $\tau$-leptons are reconstructed in their hadronic decay modes using a novel dedicated tagger for collimated $\tau$-lepton pairs. The search uses 140/fb of proton–proton collision data at a centre-of-mass energy of $\sqrt{s} = 13$ TeV recorded between 2015 and 2018 by the ATLAS experiment. The search is performed in the mass range of the $a$ boson between 10 GeV and 60 GeV.2025-11-10http://cds.cern.ch/record/2948295Physicshttp://cds.cern.ch/record/2948295oai:cds.cern.ch:2948295