Doctoral Dissertation Open Access

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

Pfeffer, Emanuel

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  <dc:creator>Pfeffer, Emanuel</dc:creator>
  <dc:date>2025-01-29</dc:date>
  <dc:description>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.</dc:description>
  <dc:identifier>https://publish.etp.kit.edu/record/22299</dc:identifier>
  <dc:identifier>oai:publish.etp.kit.edu:22299</dc:identifier>
  <dc:language>eng</dc:language>
  <dc:relation>doi:10.5445/IR/1000178528</dc:relation>
  <dc:relation>url:https://publish.etp.kit.edu/communities/cms</dc:relation>
  <dc:relation>url:https://publish.etp.kit.edu/communities/etp</dc:relation>
  <dc:rights>info:eu-repo/semantics/openAccess</dc:rights>
  <dc:subject>CERN</dc:subject>
  <dc:subject>LHC</dc:subject>
  <dc:subject>CMS</dc:subject>
  <dc:subject>particle physics</dc:subject>
  <dc:subject>top physics</dc:subject>
  <dc:subject>Higgs physics</dc:subject>
  <dc:subject>cross section measurements</dc:subject>
  <dc:subject>Machine Learning</dc:subject>
  <dc:subject>Artificial Intelligence</dc:subject>
  <dc:title>Simultaneous cross section measurements of top quark-antiquark pair production with additional heavy flavor jets at the CMS experiment</dc:title>
  <dc:type>info:eu-repo/semantics/doctoralThesis</dc:type>
  <dc:type>thesis-phd-thesis</dc:type>
</oai_dc:dc>
Publication date:
January 29, 2025
Keyword(s):
CERN LHC CMS particle physics top physics Higgs physics cross section measurements Machine Learning Artificial Intelligence
Awarding University:
Karlsruhe Institute of Technology (KIT)
Report Number:
ETP-KA/2024-11
Related identifiers:
Identical to:
10.5445/IR/1000178528
Communities:

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