Concurrent Exploration of Axion-Like Particle Interactions with Gauge Bosons at the LHC

Abstract

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.