2024

Search for short- and long-lived axion-like particles in 𝐻 → 𝑎𝑎 → 4𝛾 decays with the ATLAS experiment at the LHC

Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Acharya, B. S.; Bourdarios, C. A.; Adamczyk, L.; Addepalli, S. V.; Addison, M. J.; Adelman, J.; Adiguzel, A.; Adye, T.; Affolder, A. A.; Afik, Y.; Agaras, M. N.; Agarwala, J.; Aggarwal, A.; Agheorghiesei, C.; Ahmad, A.; Ahmadov, F.; Ahmed, W. S.; Ahuja, S.; Ai, X.; Aielli, G.; Aikot, A.; Tamlihat, M. A.; Aitbenchikh, B.; Aizenberg, I.; Akbiyik, M.; Åkesson, T. P. A.; Akimov, A. V.; Akiyama, D.; Akolkar, N. N.; Khoury, K. A.; Alberghi, G. L.

Presented is the search for anomalous Higgs boson decays into two axion-like particles (ALPs) using the full Run 2 data set of 140 fb⁻¹ of proton-proton collisions at a centre-of-mass energy of √𝒔 = 13 TeV recorded by the ATLAS experiment. The ALPs are assumed to decay into two photons, providing sensitivity to recently proposed models that could explain the (𝑔 − 2)𝜇 discrepancy. This analysis covers an ALP mass range from 100 to 62{GeV} and ALP-photon couplings in the range 10⁻⁷ TeV⁻¹ <𝐶_𝑎𝛾𝛾 / 𝚲 <1 TeV⁻¹, eV⁻¹, and therefore includes signatures with significantly displaced vertices and highly collinear photons.

No significant excess of events above the Standard Model background is observed. Upper limits at 95% confidence level are placed on the branching ratio of the Higgs boson to two ALPs in the four-photon final state, and are in the range of 10⁻⁵ to 3 × 10⁻², depending on the hypothesized ALP mass and ALP-photon coupling strength.