Speaker
Description
Axion-like particles (ALPs) are predicted in many extensions of the Standard Model (SM) and are well-motivated benchmark candidates for new physics searches at colliders. We investigate the constraints on the dimension-6 portal coupling between the ALP and the Higgs boson at the High Luminosity LHC. When the ALP mass is below half of the Higgs mass, this interaction is efficiently constrained through searches for exotic Higgs decays into a pair of ALPs. In this work, we consider the complementary case where the ALP mass is larger, and the on-shell Higgs decay is kinematically forbidden. Here, ALP production proceeds via an off-shell Higgs boson, which is relatively enhanced compared to a typical scalar thanks to the derivative couplings for the ALP. We perform a detailed phenomenological study of the sensitivity to the ALP-Higgs portal coupling in the doubly-resonant four-photon final state, considering backgrounds from both real and fake photons arising from multijet processes. The results show that the new physics scale associated with the ALP-Higgs coupling can be constrained to be above 1 TeV for ALP masses between 70 GeV and 250 GeV.