2025 Articles

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

Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboelela, M.; Aboulhorma, A.; Abramowicz, H.; Abulaiti, Y.; Acharya, B. S.; Ackermann, A.; Adam Bourdarios, C.; Adamczyk, L.; Addepalli, S. V.; Addison, M. J.; Adelman, J.; Adiguzel, A.; Adye, T.; Affolder, A. A.; Afik, Y.; Agaras, M. N.; Aggarwal, A.; Agheorghiesei, C.; Ahmadov, F.; Ahuja, S.; Ai, X.; Aielli, G.; Aikot, A.; Ait Tamlihat, M.; Aitbenchikh, B.; Akbiyik, M.; Åkesson, T. P. A.; Akimov, A. V.; Akiyama, D.; Akolkar, N. N.; Aktas, S.; Alberghi, G. L.; Albert, J.; Al Khoury, Konie

A 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.