Simultaneous cross section measurements of top quark-antiquark pair production with additional heavy flavor jets at the CMS experiment

This thesis presents a simultaneous cross section measurement of top quark-antiquark pair ($\text{t}\bar{\text{t}}$) production in association with b jets, c jets, a Higgs boson, or a Z boson in the $\text{H/Z}\to \text{b}\bar{\text{b}}$ decay mode with exactly two charged leptons (e,$\mu$), targeting the dilepton $\text{t}\bar{\text{t}}$ decay channel.

The measurement is performed at the CMS experiment at the CERN LHC in proton-proton collisions at a center-of-mass energy of $13\,\text{TeV}$ and the analyzed data corresponds to an integrated luminosity of approximately $60\,\text{fb}^{-1}$.

Collision events are modeled as a mathematical graph structure and processed using graph transformer neural network architectures based on multi-head attention mechanisms to perform multi-class classification.

The measured cross sections are parameterized as signal strength parameters relative to the cross sections predicted by the SM.

Four signal strength parameters are simultaneously extracted in a maximum likelihood fit to data and result to $\mu_{\text{t}\bar{\text{t}}\text{B}}^{\text{obs}} = 0.98^{+0.34}_{-0.25}$, $\mu_{\text{t}\bar{\text{t}}\text{C}}^{\text{obs}} = 0.74^{+0.41}_{-0.41}$, $\mu_{\text{t}\bar{\text{t}}\text{H}}^{\text{obs}} = 0.89^{+0.95}_{-0.93}$, and $\mu_{\text{t}\bar{\text{t}}\text{Z}}^{\text{obs}} = 1.28^{+1.15}_{-1.06} $, corresponding to an observed (expected) significance of $15\sigma$ ($16\sigma$) for $\text{t}\bar{\text{t}}\text{B}$, $1.8\sigma$ ($2.9\sigma$) for $\text{t}\bar{\text{t}}\text{C}$, $1.0\sigma$ ($1.1\sigma$) for $\text{t}\bar{\text{t}}\text{H}$, and $1.2\sigma$ ($1.0\sigma$) for $\text{t}\bar{\text{t}}\text{Z}$ compared to the SM prediction without these processes.

The results reveal a good agreement with the SM expectation for the signal strength of one within the 68% confidence interval.