Measurement of off-shell Higgs boson production in the H∗→ZZ→4ℓ decay channel using a neural simulation-based inference technique in 13 TeV pp collisions with the ATLAS detector

Abstract

A measurement of off-shell Higgs boson production in the HASTERISK OPERATOR RIGHTWARDS ARROWZZRIGHTWARDS ARROW4ℓ decay channel ispresented. The measurement uses 140 fb-1 of proton-proton collisions atSQUARE ROOTs = 13 TeVcollected by the ATLAS detector at the Large Hadron Collider and supersedes the previousresult in this decay channel using the same dataset. The data analysis is performed using aneural simulation-based inference method, which builds per-event likelihood ratios using neuralnetworks. The observed (expected) off-shell Higgs boson production signal strength in theZZRIGHTWARDS ARROW4ℓ decay channel at 68% CL is 0.87+0.75-0.54 (1.00+1.04-0.95). The evidence for off-shell Higgsboson production using the ZZRIGHTWARDS ARROW4ℓ decay channel has an observed (expected) significance of2.5σ (1.3σ). The expected result represents a significant improvement relative to that of theprevious analysis of the same dataset, which obtained an expected significance of 0.5σ. Whencombined with the most recent ATLAS measurement in the ZZRIGHTWARDS ARROW2ℓ2ν decay channel, theevidence for off-shell Higgs boson production has an observed (expected) significance of 3.7σ(2.4σ). The off-shell measurements are combined with the measurement of on-shell Higgsboson production to obtain constraints on the Higgs boson total width. The observed (expected)value of the Higgs boson width at 68% CL is 4.3+2.7-1.9 (4.1+3.5-3.4) MeV.