The ATLAS Collaboration has recently reported the results of a low-mass Higgs-boson search in the diphoton final state based on the full Run 2 dataset. The results are based on an improved analysis with respect to the previous analysis, which included a part of the Run 2 data, with a substantially better sensitivity. The “model-dependent” search carried out by ATLAS shows an excess of events at a mass of about 95.4 GeV with a local significance of $1.7\sigma$. The results are compatible with a previously reported excess at the same mass, but with somewhat higher significance of $2.9\sigma$, from the CMS collaboration, also based on the full Run 2 dataset. Combining the two results (neglecting possible correlations), we find a signal strength of ${\mu }_{\gamma \gamma }^{\mathrm{ATLAS}+\mathrm{CMS}}={0.24}_{-0.08}^{+0.09}$, corresponding to an excess of $3.1\sigma$. In this work, we investigate the implications of this result, updating a previous analysis based solely on the CMS Run 2 data. We demonstrate that the ATLAS/CMS combined diphoton excess can be interpreted as the lightest Higgs boson in a Two-Higgs doublet model that is extended by a complex singlet (S2HDM) of Yukawa types II and IV, while being in agreement with all other experimental and theoretical constraints.

• Received 29 July 2023
• Accepted 18 January 2024

DOI:https://doi.org/10.1103/PhysRevD.109.035005

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society