January 29, 2025 Doctoral Dissertation Open Access

Pfeffer, Emanuel

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{
  "abstract": "<p>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.</p>\n\n<p>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 $60\\,\\text{fb}^{-1}$.</p>\n\n<p>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.</p>\n\n<p>The measured cross sections are parameterized as signal strength parameters relative to the cross sections predicted by the SM.</p>\n\n<p>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.</p>\n\n<p>The results reveal a good agreement with the SM expectation for the signal strength of one within the 68% confidence interval.</p>", 
  "author": [
    {
      "family": "Pfeffer, Emanuel"
    }
  ], 
  "id": "22299", 
  "issued": {
    "date-parts": [
      [
        2025, 
        1, 
        29
      ]
    ]
  }, 
  "language": "eng", 
  "title": "Simultaneous cross section measurements of top quark-antiquark pair production with additional heavy flavor jets at the CMS experiment", 
  "type": "thesis"
}