Search for Higgs Boson Production in Association with b-Quarks in Final States with Leptons with Machine Learning Techniques at CMS

One of the primary objectives of the CMS experiment is to measure the mechanisms of the Higgs boson production precisely and to determine its coupling structure. The Yukawa interaction is the mechanism via which the Higgs boson couples to fermions in the Standard Model. Due to the small cross-section and the very large background processes, the Yukawa coupling to b-quarks ($y_{b}$) has only been measured in the decay process and not in the production mechanism. The present work is devoted to analysing the Higgs boson production in association with b-quarks in final states with leptons. The search for Higgs boson decays to tau leptons and W bosons was performed using data collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV during LHC Run 2. The final states covered in this search are those in which the Higgs boson is produced via the bbH channel and decays into two tau leptons, which subsequently decay either fully hadronically ($\tau_{h}\tau_{h}$), semi-leptonically ($\tau_{e}\tau_{h} $, $\tau_{\mu}\tau_{h}$), or fully leptonically ($\tau_{e}\tau_{ \mu}$). The latter channel is also studied from the decay of Higgs boson into two W bosons. The fully leptonic channel is the primary focus of this work, and as such, it will be described extensively. Other channels will be briefly presented to discuss the combination of the results. This analysis employs machine learning techniques to improve the sensitivity to the signal process, which brings almost factor 2 improvement with respect to the traditional cut-based approach. Final constraints are derived on the Higgs boson production cross section as an upper limit on the signal strength of the process. The observed (expected) upper limits on the signal strength modifier obtained for the fully leptonic channel for the Run 2 data is 18.7 (19.1) times the Standard Model prediction at 95$\%$ confidence level. For the combination of all the channels, fully hadronically ($\tau_{h}\tau_{h}$), semi-leptonically ($\tau_{e}\tau_{h} $, $\tau_{\mu}\tau_{h}$), fully leptonically ($\tau_{e}\tau_{ \mu}$), the upper limit at 95$\%$ confidence level is observed (expected) to be 3.7 (6.1) times the Standard Model prediction. Furthermore, constraints on the Higgs Yukawa coupling to the b-quark are determined in the kappa model interpretation, and the results are consistent with the Standard Model.