Explanation of the excesses in associated di-photon production at 152 GeV in 2HDM

Statistically significant excesses exist at around 152 GeV in associated di-photon production (γγ+X) in the sidebands of SM Higgs analyses of ATLAS (using the full run-2 dataset). They are most pronounced in the single-τ, missing-transverse-energy, four-jet and 1+\!1b-jet channels (≈3σ) and can be explained by the Drell-Yan production of new Higgs bosons, i.e. pp→ W^*→ H^± H⁰. We first examine the excesses in a simplified model approach, considering that H^± decays to τν, $WZ$ or $tb$. Both the τν and $tb$ decay modes individually lead to a significance of 4σ while for $WZ$ one can obtain at most 3.5σ. This is because the decays of $WZ$ lead to multiple leptons contributing to the two-lepton channel which does not show an excess at 152 GeV. Next, we consider two-Higgs-doublet models where the charged Higgs does not decay to $WZ$ at tree-level, finding a significance of 4σ for a branching ratio of the new neutral Higgs to photons of ≈2%. Even though this branching fraction is quite sizable, it can be obtained in composite models or via the Lagrangian term λ₆ H₁^ H₁ H₂^ H₁+ h.c. breaking the commonly imposed Z₂ symmetry.