Search for Higgs boson decays into a $Z$ boson and a light hadronically decaying resonance using 13 TeV $pp$ collision data from the ATLAS detector

Understand

A search for Higgs boson decays into a $Z$ boson and a light resonance in two-lepton plus jet events is performed, using a $pp$ collision dataset with an integrated luminosity of 139 fb$^{-1}$ collected at $\sqrt{s}=13$ TeV by the ATLAS experiment at the CERN LHC.

• The resonance considered is a light boson with a mass below 4 GeV from a possible extended scalar sector, or a charmonium state.
• Multivariate discriminants are used for the event selection and for evaluating the mass of the light resonance.
• No excess of events above the expected background is found.