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 ($\text{t}\overline{\text{t}}$) production in association with b jets, c jets, a Higgs boson, or a Z boson in the $\text{H/Z}\to \text{b}\overline{\text{b}}$ decay mode with exactly two charged leptons (e,$\mu$), targeting the dilepton $\text{t}\overline{\text{t}}$ 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 ${\mu }_{\text{t}\overline{\text{t}}\text{B}}^{\text{obs}}={0.98}_{-0.25}^{+0.34}$, ${\mu }_{\text{t}\overline{\text{t}}\text{C}}^{\text{obs}}={0.74}_{-0.41}^{+0.41}$, ${\mu }_{\text{t}\overline{\text{t}}\text{H}}^{\text{obs}}={0.89}_{-0.93}^{+0.95}$, and ${\mu }_{\text{t}\overline{\text{t}}\text{Z}}^{\text{obs}}={1.28}_{-1.06}^{+1.15}$, corresponding to an observed (expected) significance of $15\sigma$ ($16\sigma$) for $\text{t}\overline{\text{t}}\text{B}$, $1.8\sigma$ ($2.9\sigma$) for $\text{t}\overline{\text{t}}\text{C}$, $1.0\sigma$ ($1.1\sigma$) for $\text{t}\overline{\text{t}}\text{H}$, and $1.2\sigma$ ($1.0\sigma$) for $\text{t}\overline{\text{t}}\text{Z}$ compared to the SM prediction without these processes.
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The results reveal a good agreement with the SM expectation for the signal strength of one within the 68% confidence interval.