Measurement of ttH(H→bb) production in the semi-leptonic tt decay channel at the CMS Experiment

Abstract

A measurement of the production of a Higgs boson in association with a top quark-antiquark pair and the subsequent decay of the Higgs boson to a bottom quark-antiquark pair ($\text{t}\bar{\text{t}}\text{H}(\text{H}\rightarrow \text{b}\bar{\text{b}})$) at a center-of-mass energy of $13\,\text{TeV}$ is presented. The measurement focuses on the semileptonic decay channel of the top quark-antiquark pair and is based on proton-proton collision data recorded by the CMS Experiment in the years 2016 and 2017 corresponding to an integrated luminosity of $77.4\,\text{fb}^{-1}$. The cross section for the production of a Higgs boson in association with a top quark-antiquark pair ($\text{t}\bar{\text{t}}\text{H}$) depends on the top-Higgs Yukawa coupling and a measurement of $\text{t}\bar{\text{t}}\text{H}$ production provides direct access to this important property of the standard model of particle physics. To achieve the measurement of this process, candidate $\text{t}\bar{\text{t}}\text{H}(\text{H}\rightarrow \text{b}\bar{\text{b}})$ events are first selected from the analyzed data. Artificial neural networks are then used to construct observables that allow the discrimination between signal and background processes. To extract the signal contribution in data, standard model predictions for these observables are fit to data using a profile likelihood approach. This results in a best-fit value for the signal strength relative to the standard model prediction $\mu = \sigma/\sigma_{\text{SM}}$ of \begin{equation} \hat{\mu} = 1.22^{+0.41}_{-0.37}({\text{tot.}}) \left[{}^{+0.19}_{-0.19}({\text{stat.}}) {}^{+0.36}_{-0.32}({\text{syst.}}) \right]. \end{equation} This result is compatible with the standard model prediction and corresponds to an observed (expected) significance of $3.3$ ($2.7$) standard deviations with respect to the background-only hypothesis. In addition, combined analyses performed by the CMS Collaboration are discussed, in which analyses of various production and decay modes of the Higgs boson were statistically combined. The presented anylsis of $\text{t}\bar{\text{t}}\text{H}(\text{H}\rightarrow \text{b}\bar{\text{b}})$ production in the semileptonic channel was an important contribution to theses combinations, which resulted in the observation of $\text{t}\bar{\text{t}}\text{H}$ production and of the $\text{H}\rightarrow \text{b}\bar{\text{b}}$ decay mode.