Abstract : The Standard Model (SM) of particle physics has been remarkably successful in describing fundamental interactions, yet it leaves several open questions, motivating searches for physics beyond the Standard Model (BSM). In this study, we present a search for Higgs boson and additional scalar decays into BSM light bosons, such as dark photons or pseudoscalars, which subsequently decay into four-lepton final states, using data collected by the ATLAS experiment at the Large Hadron Collider (LHC). These decays are predicted in several BSM scenarios, including the Higgs-Abelian Hidden Model (HAHM), two-Higgs doublet models with an additional singlet (2HDM+S), and hidden valley models. The analysis employs advanced lepton reconstruction techniques, multivariate discriminators, and optimized selection criteria to enhance sensitivity to these rare signatures. The results are interpreted within the HAHM framework and other benchmark models, setting constraints on the production cross-section and branching ratios of the hypothesized light bosons. No significant deviation from the SM is observed, providing new insights into extended scalar sectors and hidden forces, and guiding future searches for exotic Higgs decays.
Peter Gaemers (pgaemers@slac), Sayan Ghosh (sghosh92@slac), Jamie Ryan (jlryan@slac)
