% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@PHDTHESIS{Otto:276667,
      author       = {Otto, Jan-Hendrik},
      othercontributors = {Höhne, Claudia},
      title        = {{D}ielectron reconstruction in {A}g+{A}g collisions at
                      $\sqrt{s_{{NN}}}$ = 2.55 {G}e{V} with {HADES}},
      school       = {Justus Liebig University Giessen},
      type         = {Dissertation},
      publisher    = {Universitätsbibliothek Gießen},
      reportid     = {GSI-2023-00286},
      pages        = {224 p.},
      year         = {2022},
      note         = {Dissertation, Justus Liebig University Giessen , 2022},
      abstract     = {The study of strongly interacting matter under extreme
                      conditions in terms of temperature and pressure has moved
                      more and more in the focus of high energy physics over the
                      last decades. These conditions can be created in the
                      collision of heavy-ions at various facilities around the
                      world, together covering a broad range of collision energies
                      starting in the GeV region and ranging up to energies of
                      several TeV. In order to study the medium created in such
                      collisions and get an insight in the underlying processes,
                      dileptons are ideal messengers as they do not interact
                      strongly and can therefore leave the medium unharmed
                      carrying their initial properties to the particle detectors.
                      They thus reveal the thermal conditions and the lifetime of
                      the medium but also give insights into meson properties at
                      high densities. One of the experiments dedicated to the
                      investigation of strongly interacting matter is the High
                      Acceptance DiElectron Spectrometer (HADES). It is a
                      versatile detector with particular focus on dielectron
                      measurements in pion, proton, deuteron and (heavy-)
                      ion-induced reactions using proton or nucleus targets in the
                      SIS-18 energy range (1-2 GeV/nucleon). Its excellent
                      particle identification capabilities also allow for the
                      investigation of hadronic observables. The analysis of a
                      high statistics sample of Ag+Ag collisions (4.5 billion
                      events for 0 - 40 $\%$ centrality) at $sqrt(s_NN)$ = 2.55
                      GeV measured by HADES is presented with respect to
                      dielectron production in this work. The recently upgraded
                      HADES RICH detector leads to an unprecedented quality and
                      signal-to-background ratio in the detection of these
                      extremely rare probes. Due to the large number of
                      reconstructed Cherenkov photons it is possible for the first
                      time ever, to efficiently identify and reject electrons
                      produced in conversion processes by a simple count of
                      measured photons. The obtained dielectron spectrum shows a
                      signal up to the phi meson mass region and is compared to
                      simulated hadronic cocktail and nucleon-nucleon reference
                      spectra revealing a strong contribution from the hot and
                      dense phase quantified by the dielectron excess ratio
                      $R_AA.$ The multiplicities of the hadrons are estimated in
                      an analysis of the decay channels $pi^0/eta$ -> 2 gamma ->
                      4e and omega -> e+e- in the same data set. The slope of the
                      in-medium contribution allows for the extraction of the mean
                      medium temperature. A differential analysis in bins of
                      centrality enables the study of these observables in
                      dependence on the system size. Furthermore, a differential
                      analysis in pair momentum is performed showing a significant
                      change in the line-shape of the spectrum in the rho-omega
                      mass region with increasing (transverse) pair-momentum which
                      suggests a substantial modification of the meson properties
                      in the medium. Previous HADES measurements of Au+Au
                      collisions at $sqrt(s_NN)$ = 2.42 GeV and Ar+KCl at
                      $sqrt(s_NN)$ = 3.18 GeV provide data for comparison and to
                      study energy and system-size dependence of the obtained
                      results. In the second part of this work the calculation of
                      spectral functions with the Functional Renormalization Group
                      (FRG) including one-loop self-energies in a self consistent
                      way is presented. Spectral functions are defined as the
                      imaginary part of the electromagnetic current-current
                      correlation function and provide direct access to thermal
                      photon and dilepton rates. The calculations are performed
                      for the pion and the sigma meson in the O(4) model at
                      vanishing temperature in the chirally broken phase.
                      Comparing the results with those from previous analytically
                      continued FRG calculations, it is demonstrated, how
                      self-consistency at all momenta fixes the relation between
                      particle masses and decay thresholds.},
      keywords     = {ddc:530 (Other)},
      cin          = {HAD / HADES@GSI},
      cid          = {I:(DE-Ds200)HAD-20080822OR103 / I:(DE-Ds200)Coll-GSI-HADES},
      pnm          = {612 - Cosmic Matter in the Laboratory (POF4-612) /
                      SUC-GSI-Giessen - Strategic university cooperation GSI-U
                      Gießen (SUC-GSI-GI) / HGS-HIRe - HGS-HIRe for FAIR
                      (HGS-HIRe)},
      pid          = {G:(DE-HGF)POF4-612 / G:(DE-Ds200)SUC-GSI-GI /
                      G:(DE-Ds200)HGS-HIRe},
      experiment   = {EXP:(DE-Ds200)S477-20200803},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.22029/JLUPUB-7207},
      url          = {https://repository.gsi.de/record/276667},
}