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@PHDTHESIS{Mller:349744,
      author       = {Müller, Julian},
      othercontributors = {Denig, Achim},
      title        = {{M}easurement of the electromagnetic form factors of the
                      proton via elastic scattering in the {Q}$^2$ range from 0.5
                      to 2 ({G}e{V}/c)$^2$},
      school       = {Johannes Gutenberg-Universität Mainz},
      type         = {Dissertation},
      reportid     = {GSI-2024-00487},
      pages        = {137 p.},
      year         = {2024},
      note         = {Dissertation, Johannes Gutenberg-Universität Mainz, 2023},
      abstract     = {The electric and magnetic form factor of the proton are
                      connected to the distributionof electric charge and electric
                      current inside the proton. As a fundamentalproperty of the
                      proton, the knowledge of the form factors therefore allows
                      to gaininsight into the structure of the proton. The form
                      factors are accessible in elasticelectron-proton scattering
                      experiments, which have been performed since the1950s. One
                      distinguishes two types of experiments, the scattering with
                      polarizedand unpolarized electrons. Around the turn of the
                      millennium, it was found thatthere is a discrepancy in the
                      electric to magnetic form factor ratio of the
                      protonGE(Q2)/GM(Q2), when comparing the results of both
                      methods. According to thedata from polarization experiments,
                      the ratio follows a linear decreasing trend withincreasing
                      momentum transfer Q2, whereas the ratio measured in
                      unpolarized scatteringremains roughly constant. The commonly
                      assumed explanation for this discrepancyis the contribution
                      of the two photon exchange (TPE) to the scatteringprocess,
                      which has a different influence on polarized and unpolarized
                      scattering.To investigate the discrepancy in the form factor
                      ratio and the influence of the TPE,new unpolarized elastic
                      electron-proton scattering data were measured at the
                      MainzMicrotron MAMI and the 3-spectrometer-facility of the
                      A1 collaboration. The datawere taken at seven beam energies
                      between 720MeV and 1508MeV to cover the Q2region from 0.5
                      (GeV/c)2 to 2 (GeV/c)2. The new data extends an already
                      existingdata set from an earlier measurement in 2010. In
                      total, the MAMI data set nowconsists of 1676 cross section
                      points in the Q2 range between 0.004 (GeV/c)2 and2 (GeV/c)2.
                      The measured cross sections were corrected for radiative
                      processes byutilizing an extensive simulation, which
                      calculates the radiative corrections for eachevent. Instead
                      of using the classical Rosenbluth technique, the MAMI data
                      set wasanalyzed via a direct fit of a form factor model to
                      the cross section data to separatethe form factors. The
                      fitting procedure was also used to determine the
                      normalizationof the data, however, the fit proved to have
                      stability issues for the data at higherbeam energies. The
                      inclusion of external data from previous unpolarized
                      experimentsprovided the stability needed for the fit and an
                      excellent agreement betweenthe two parts of the MAMI data
                      set could be demonstrated. Two different modelsfor the TPE
                      correction were applied to the data before the fit, to
                      investigate by howmuch the contribution shifts the form
                      factors. The extracted form factor ratio fromthe fit was
                      compared to the data from polarization experiments.The
                      results showed that the MAMI data produce a linear
                      decreasing form factorratio, independently of the applied
                      TPE model. This trend has not been observedin previous
                      unpolarized experiments. An overall lower electric to
                      magnetic formfactor ratio in unpolarized electron-proton
                      scattering could play an important rolein solving the
                      discrepancy between polarized and unpolarized experiments.},
      cin          = {MSF},
      cid          = {I:(DE-Ds200)MSF-20150313OR331},
      pnm          = {612 - Cosmic Matter in the Laboratory (POF4-612)},
      pid          = {G:(DE-HGF)POF4-612},
      experiment   = {$EXP:(DE-Ds200)External_experiment-20200803$},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:hebis:77-openscience-d78516b5-91aa-48aa-8158-5cce33f00e122},
      url          = {https://repository.gsi.de/record/349744},
}