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@PHDTHESIS{GonzalezRodrigues:641372,
      author       = {Gonzalez Rodrigues, Marcus},
      othercontributors = {Gallo-Voss, Elisabetta and Behr, Janna Katharina},
      title        = {{S}earch for the production of a pair of highly
                      {L}orentz-boosted {H}iggs bosons via vector-boson fusion in
                      final states with four bottom quarks with the {ATLAS}
                      experiment},
      school       = {University of Hamburg},
      type         = {Dissertation},
      reportid     = {PUBDB-2025-05033},
      pages        = {188},
      year         = {2025},
      note         = {Dissertation, University of Hamburg, 2025},
      abstract     = {A search for the production of a pair of Higgs bosons
                      ($HH$) via vector-boson fusion (VBF) in the Lorentz-boosted
                      kinematic regime with subsequent decay of the Higgs bosons
                      into four bottom quarks is presented. The analysis is based
                      on 140~fb$^{-1}$ of proton-proton collision data collected
                      with the ATLAS detector at the Large Hadron Collider (LHC),
                      at a center-of-mass energy of $\sqrt{s} = 13$~TeV. The
                      results were interpreted in terms of both non-resonant and
                      resonant production of Higgs-boson pairs. Non-resonant VBF
                      $HH$ production is predicted by the Standard Model (SM); the
                      production cross-section is, however, significantly enhanced
                      for anomalous, non-SM values for the trilinear Higgs-boson
                      self-coupling and the quartic coupling between two Higgs
                      bosons and two vector bosons, parametrised as $\kappa_{\l}$
                      and $\kappa_{2V}$, respectively. Resonant VBF $HH$
                      production is predicted only by extensions of the SM. In
                      this thesis, the resonant $HH$ production via the decay of a
                      new heavy scalar particle originating from the vector-boson
                      scattering was considered. No significant deviation of the
                      data from the expected background was observed. Hence, in
                      the non-resonant search, limits on the $\kappa_{2V}$ and
                      $\kappa_{\l}$ couplings were set at $95\\%$ confidence
                      level. In the resonant search, upper limits on the signal
                      cross-section were derived for intermediate masses ranging
                      from 1.0~TeV to 5.0~TeV under the assumptions of a narrow-
                      and broad-resonance widths. In the model-dependent
                      broad-width scenario, a composite Higgs benchmark has been
                      considered. In addition to these results, which have been
                      published in 2024, the relevant details of a successive
                      on-going ATLAS analysis using additionally data collected in
                      2022 and 2023 at $\sqrt{s} = 13.6$~TeV and using more modern
                      tools to identify the $H \to b\bar{b}$ decays is discussed
                      here. Finally, a proof-of-principle study using a
                      transformer-based machine-learning algorithm to discriminate
                      signal from background events in triple Higgs-boson searches
                      is also shown in this thesis. The even rarer production of
                      three Higgs bosons has been gaining significant interest
                      since it provides unique access to the quartic Higgs-boson
                      self-coupling.},
      keywords     = {530: Physik (autogen)},
      cin          = {ATLAS},
      cid          = {I:(DE-H253)ATLAS-20120731},
      pnm          = {611 - Fundamental Particles and Forces (POF4-611)},
      pid          = {G:(DE-HGF)POF4-611},
      experiment   = {EXP:(DE-H253)LHC-Exp-ATLAS-20150101},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:gbv:18-ediss-130726},
      doi          = {10.3204/PUBDB-2025-05033},
      url          = {https://bib-pubdb1.desy.de/record/641372},
}