Evidence of the off-shell Higgs and Higgs decay width constraints at ATLAS

This paper reports a search for off-shell Higgs boson production and the measurement of the Higgs decay width using the full Run-2 pp collision dataset, corresponding to an integrated luminosity of 139 fb(-1), collected by the ATLAS detector at the Large Hadron Collider. In this analysis, the Higgs boson production modes include gluon-gluon fusion, vector-boson fusion, and VH, while the Higgs boson decay channels ZZ -> 4l and ZZ -> 2l2v (l = e or mu) are considered. The background-only hypothesis is rejected at the confidence level of 3.3 sigma (2.2 sigma) for the observed (expected) result, providing evidence of the off-shell Higgs boson. The combination of the off-shell and on-shell Higgs boson measurements can constrain the Higgs decay width to be 4.5(-2.5)(+3.3) MeV, with an upper limit of 10.5 MeV at the 95% confidence level.