The CMS experiment at CERN has conducted a search for light-weight hypothetical particles, specifically axion-like particles (ALPs), that may result from Higgs boson decays. These ALPs are theorised to decay into electron-positron pairs, which present a significant challenge for detection due to their merged experimental footprints. To overcome this, the CMS Collaboration developed a new multivariate identification technique using machine learning and precise tracking data. While no significant excess beyond the Standard Model was observed, the research established new stringent limits on exotic Higgs boson decays, thus providing crucial constraints on theoretical models of ALPs and demonstrating the LHC's unique capacity for exploring new physics.

CMS Physics Analysis Summary (EXO-24-031): "Search for light pseudoscalar a bosons in H→aa→4e decays in pp collisions at √s = 13 TeV"