Speaker
Description
The production of a Higgs boson in association with a single top quark (tH) provides a unique probe of the Higgs-top Yukawa coupling due to the interference between diagrams involving the Higgs coupling to the top quark and to vector bosons. As a result, this process is particularly sensitive to both the magnitude and the sign of the top Yukawa coupling, making it a powerful test of the Standard Model and a potential window to new physics.
This contribution presents the combined search for tH production performed by the ATLAS Collaboration using the full Run-2 proton-proton collision dataset collected at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 140 fb⁻¹. The combination includes several complementary final states targeting Higgs boson decays into bb, WW, ZZ, and ττ, exploiting signatures with one or more charged leptons, including hadronically decaying τ leptons plus tH production in the H→𝛾𝛾 decay mode. Advanced multivariate techniques are employed to enhance the separation between signal and background processes.
Evidence for the process is not yet established. However, the combination yields an observed significance of 2.3 standard deviations above the background-only hypothesis. An observed upper limit at 95% confidence level of 8.5 times the Standard Model prediction is set on the tH production rate. These results represent the most sensitive ATLAS search for tH production using the full Run-2 dataset.