Inclusive and differential cross-section measurements of four-lepton production in $\sqrt{s}=13$ TeV proton-proton collisions with the ATLAS detector

Recent measurements of inclusive four-lepton production in $\sqrt{s} = 13$ TeV proton-proton collisions at the Large Hadron Collider (LHC) are presented. The data corresponds to an integrated luminosity of 139 fb$^{−1}$, collected by the ATLAS detector during Run 2 of the LHC (2015-2018). Inclusive and differential fiducial cross-sections for events with two same-flavour, opposite-charge electron or muon pairs are measured. The four-lepton final state exhibits a complex structure with contributions from several Standard Model processes, including single Z production, Higgs production, and on-shell ZZ production, with possible contributions from Beyond-the-Standard-Model (BSM) physics. The four-lepton invariant mass is measured inclusively and differentially in slices of other four-lepton kinematic variables. Pair-specific observables, including di-lepton invariant masses, pair separation, and angular correlation variables, are measured in four slices of four-lepton invariant mass, each targeting a different production mode. The measurements are corrected for detector effects and compared to state-of-the-art Standard Model predictions, which are found to be consistent with the data. Using the detector-corrected data, the single $Z\to4\ell$ branching fraction is extracted, yielding a value of $(4.41 \pm 0.30)\times10^{−6}$. Additionally, constraints on effective field theory parameters and a BSM model based on a spontaneously broken B-L gauge symmetry are evaluated. Many further re-interpretations are promising given the inclusive nature of the analysis and the wide variety of measured observables.