Search for off-shell production of the Higgs boson and measurement of its total width with the ATLAS experiment

This talk presents a search for off-shell production of the Higgs boson using 139 fb-1 of pp collision data at sqrt(s) = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The observable signature is a pair of on-shell Z bosons, with contributions both from the virtual Higgs bosons and interference with other processes, and the two decay final states, ZZ->4l and ZZ->2l2nu with l = e or mu. The background-only hypothesis is rejected with an observed (expected) significance of 3.2 (2.4) sigmas which marks the experimental evidence of off-shell Higgs production. The observed (expected) upper limit on the signal strength, defined as the event yield normalised to the Standard Model prediction is 2.3 (2.4) at 95% confidence level, which restricts the total width of the Higgs boson to be less than 9.7 (10.2) MeV at the same confidence level. The off-shell Higgs (220 GeV < mH < 2000 GeV) provides a pivotal window to search for BSM hints. The corresponding EFT interpretations for Higgs-gluon and Higgs-top quark interactions are possibly provided.