Concurrent exploration of Axion-like particle interactions with gauge bosons at the LHC

Axion-like particles (ALPs) are pseudo Nambu-Goldstone bosons associated with spontaneously broken global symmetries incorporated in the Standard Model (SM) Lagrangian in many models beyond the SM. The existence of a light ALP is plausible due to the long-standing problems that the SM has not been able to address, such as the dark matter (DM) problem and the observed matter-antimatter asymmetry. There are many proposals in recent decades considering the ALP as a solution to some of these shortcomings. Motivated by such potential, we search for ALPs with a mass of 1 MeV at the LHC in a model-independent fashion. We explore two complementary production modes: ALP production in association with a pair of electroweak gauge bosons (ZZ or WW) and ALP production in association with a single gauge boson (W or Z) plus jets. For the VV+a final state, signal and dominant SM backgrounds are generated, and a realistic detector response simulation is performed. A multivariate analysis is employed to discriminate the VV+a signal from background processes, and the expected 95% confidence level (CL) exclusion limits in two-dimensional parameter spaces involving the ALP couplings are subsequently derived. The V+jets channel is interpreted using LHC measurements in regimes where the ALP escapes detection, appearing as missing energy. The two analyses are complementary: both the VV+a and the V+jets channels probe simultaneously the ALP couplings to gluons and to electroweak gauge bosons. While the VV+a channel offers clean multi-lepton final states and direct reconstruction of the ZZ or WW system, the V+jets channel benefits from larger production cross sections, enabling stronger constraints in certain regions of the parameter space. Comparing the limits obtained in this study with current and projected limits derived from LHC searches, it is seen that competitive sensitivities to the ALP couplings are achieved, and a significant region of previously unexplored parameter space becomes accessible.