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@MASTERSTHESIS{Roscher:615857,
      author       = {Roscher, Lukas},
      othercontributors = {Moenig, Klaus and Lacker, Heiko},
      title        = {{S}tudien zur {R}ekonstruktion der invarianten {M}asse von
                      {T}op-{A}ntitop-{P}aaren im dileptonischen {K}anal mit
                      {H}ilfe eines neuronalen {N}etzwerkes am {ATLAS}
                      {D}etektor.},
      school       = {Humboldt Universität zu Berlin},
      type         = {Masterarbeit},
      reportid     = {PUBDB-2024-06298},
      pages        = {71},
      year         = {2024},
      note         = {Masterarbeit, Humboldt Universität zu Berlin, 2024},
      abstract     = {The studies in this thesis are motivated by the measurement
                      of the top quark Yukawa coupling Ytrelative to the SM value
                      in the dileptonic decay channel of top-antitop (t¯t) pairs
                      at the ATLAS experiment. The used (simulated) data
                      correspond to the proton-proton collision data recorded
                      between 2015 and 2018 at √s=13 TeV with an integrated
                      luminosity of 140 fb−1. In the dileptonic channel, the
                      t¯t pair decays into two b quarks and two W bosons, which
                      then decay into one lepton and neutrino each. Virtual
                      corrections through the exchange of a Higgs boson between
                      the produced top quarks modify the spectrum of the invariant
                      mass of the top-antitop pair mt¯t in the region of the
                      production threshold (≈2mt). A precise analysis of this
                      distribution provides insights into the strength of the
                      top-Yukawa coupling. Due to the two neutrinos in the final
                      state, the reconstruction of mt¯t is only possible through
                      approximation methods that incorporate kinematic constraints
                      on the W mass and top quark mass as well as the
                      reconstructed missing transverse momentum. Therefore, a
                      neural network using techniques from the field of deep
                      learning is motivated and presented in this thesis, which
                      reconstructs mt¯t through regression using high-level
                      observables as input. As inputs, the invariant masses meμ,
                      meb1, meb2, mμb1, mμb2, and mb1b2 of the electrons, muons,
                      and b-jets in the final state, together with the magnitude
                      of the missing transverse momentum EmissT, are used. The
                      output distribution of the neural network is analyzed for
                      datasets generated by pythia8 and Herwig7 to investigate the
                      influence of different t¯t modeling. Additionally, the
                      agreement between simulation and experimental data is
                      examined. A maximum-likelihood fit for a future measurement
                      of Yt is presented. Here, the experimental data and the
                      expected t¯t signal for different values of Yt are
                      compared, and the best agreement is given as an estimate for
                      Yt, considering systematic uncertainties. Since the
                      systematic uncertainties were not implemented due to time
                      constraints, an initial fit based on Asimov data is
                      performed to estimate the measurement precision. Compared to
                      the easily reconstructed invariant mass mrecobbll of the
                      leptons and b-jets, the distribution from the neural network
                      shows an approximately $3.5\%$ lower uncertainty in the
                      estimation of Yt (excluding systematics). The systematic
                      uncertainty of the t¯t modeling differences by Pythia8 and
                      Herwig7 is also examined.},
      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)19},
      url          = {https://bib-pubdb1.desy.de/record/615857},
}