UC Santa Cruz

A search for the Standard Model Higgs boson produced in association with a high energy photon is performed using 133 fb−1 of pp collision data collected at √s = 13 TeV with the ATLAS detector at the Large Hadron Collider at CERN. The H + photon final state is particularly promising to study because the photon requirement reduces the multijet background, and the bb final state is the dominant decay mode of the Higgs boson. Event selection requirements isolate vector boson fusion Higgs production, the dominant production mode in this channel. Several improvements enhance the search sensitivity compared to previous measurements, including better background modeling and characterization, use of a dense neural network classifier, and an updated signal extraction strategy adopting a binned-likelihood fit directly to the classifier discriminant. These advancements result in a Higgs boson signal strength measured as 0.2 ± 0.7 relative to the Standard Model prediction. This corresponds to an observed significance of 0.3 standard deviations, compared to 1.5 standard deviations expected signal significance.