Leeuw, LerothodiAad, GeorgesAakvaag, Erlend2026-01-122026-01-122025Aad, G., Abbott, B., Abdelhameed, S., Abeling, K., Abicht, N.J., Abidi, S.H., Aboelela, M., Aboulhorma, A., Abramowicz, H., Abulaiti, Y. and Acharya, B.S., 2025. Search for Higgs boson decays into a pair of pseudoscalar particles in the γγτhadτhad final state using pp collisions at $$\sqrt {\textrm {s}} $$= 13 TeV with the ATLAS detector. Journal of High Energy Physics, 2025(3), pp.1-39.https://doi.org/10.1007/JHEP03(2025)190https://hdl.handle.net/10566/21658A search for exotic decays of the 125 GeV Higgs boson into a pair of new spin-0 particles, 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 a dedicated tagger for collimated τ-lepton pairs. The search uses 140 fb−1 of proton-proton collision data at a centre-of-mass energy of s = 13 TeV recorded between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider. The search is performed in the mass range of the a boson between 10 GeV and 60 GeV. No significant excess of events is observed above 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 γγττ final state, B(H → aa → γγττ), ranging from 0.2% to 2%, depending on the a-boson mass hypothesis.enHadron-Hadron ScatteringExotic Higgs decaysPhoton pair and τ-lepton pair final statesATLAS experimentModel-independent upper limits on branching ratioArticle