Probing the Higgs b-quark coupling ($y_b$) at the ATLAS experiment: bbH Search Feasibility Study

This CERN Summer Student Program project focuses on probing the Higgs boson’s bottom Yukawa coupling ($y_b$) through the associated production of a Higgs boson with two b-quarks (bbH). The bbH production cross section is approximately 0.5 pb at $\sqrt{s} = 13~\mathrm{TeV}$ at the LHC and have some destructive interference contributions from other Higgs production processes such as gluon-gluon Fusion (ggH) and Higgs Strahlung (VH). While the decay channel is $H \to b\Bar{b}$ have the largest branching ratio, its precision is limited by the resolution to $\mathcal{O}(10\%)$. The decay channel for this search is $H\to \gamma\gamma$ to avoid the resolution limitation since photon measurement in the ATLAS detector has a resolution of about $\mathcal{O}(1\%)$. In this feasibility study, Run 2 and Run 3 samples from the $HH\to b\Bar{b}\gamma\gamma$ analysis are used. The analysis utilizes kinematic selections, newly engineered discriminating variables, and boosted decision trees to enhance signal-background separation. Statistical sensitivity is assessed through binned significance and maximum-likelihood fits. The findings indicate limited sensitivity with the current samples, methods, and channel, highlighting the need for increased signal statistics, improved forward b-tagging, and advanced background separation.