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@PHDTHESIS{Vollbrecht:362228,
      author       = {Vollbrecht, Moritz Cornelius},
      othercontributors = {Ludhová, Livia and Stahl, Achim},
      title        = {{S}oftware and hardware development for the liquid
                      scintillator detector {OSIRIS} of the {JUNO} experiment},
      school       = {RWTH},
      type         = {Dissertation},
      publisher    = {RWTH Aachen University},
      reportid     = {GSI-2025-01092},
      pages        = {355 p.},
      year         = {2024},
      note         = {Dissertation, RWTH, 2024},
      abstract     = {The Jiagmen Underground Neutrino Observatory (JUNO) is a
                      next-generation liquid scintillator (LS) neutrino experiment
                      currently under construction near Kaiping, Southern China.
                      The construction of JUNO will end in 2024. JUNO will
                      accomplish its main goal with six years of data-taking: the
                      determination of the neutrino mass ordering with a
                      sensitivity of 3-4 $\sigma$. To achieve this goal, the LS
                      used in JUNO must meet stringent requirements regarding its
                      radiopurity. For validation of these requirements during the
                      months-long filling of JUNO, the Online Scintillator
                      Internal Radioactivity System (OSIRIS) monitors the LS
                      radiopurity via $^{214}$Bi-$^{214}$Po /
                      $^{212}$Bi-$^{212}$Po coincident decays in the respective
                      decay chains of $^{238}$U and $^{232}$Th. In OSIRIS, German
                      workgroups have a leading role. This thesis presents
                      contributions to the development of both hardware and
                      software for OSIRIS. The hardware-focused part of the thesis
                      details the author's construction of an
                      ultrapure-water-based cleaning facility at RWTH Aachen as
                      well as the design of a holder structure for OSIRIS's
                      photomultiplier tubes (PMTs). The cleaning facility was used
                      successfully to prepare many German working groups'
                      contributions prior to their shipment to China. The holder
                      development was aided by simulations based on finite element
                      analysis. Both holder design requirements and simulation
                      results were confirmed in load tests of the holder
                      structure, first at RWTH and later again on-site at JUNO in
                      2022. The holder as originally planned for the intelligent
                      PMT system (iPMT) had to be adapted at JUNO to accommodate
                      the Chinese Large PMT system (LPMT), because the iPMTs were
                      found to be non-functional upon arrival at JUNO. During the
                      on-site mission in 2022, also studies of airborne and
                      surface dust levels within the OSIRIS detector were carried
                      out by the author. The investigations proved that a)
                      OSIRIS's air filtration unit maintained the required ISO-7
                      clean room environment and b) the accumulated dust on
                      OSIRIS's central vessel was uncritical for the experiment's
                      future. The measurements also showed a substantial decrease
                      in surface particle counts after a subsequent detector
                      cleaning. The commissioning of one of OSIRIS's calibration
                      systems, the Automated Calibration System (ACU), was
                      supervised by the author in 2023 as another part of the
                      hardware-related work described here. The ACU contains a
                      radioactive multi-gamma source
                      ($^{137}$Cs/$^{65}$Zn/$^{60}$Co) and a 435 nm LED to perform
                      calibrations of LPMT timing and charge as well as
                      calibrations of detector energy and vertex reconstructions.
                      A $^{40}$K-source serves as a standard candle during normal
                      operation and is used to monitor the optical properties of
                      the LS. During the ACU commissioning, the ACU hardware and
                      software, the related safety mechanisms, and the positioning
                      of the sources were evaluated. In the positioning
                      calibrations, a precision of $\approx$4 mm was achieved,
                      which is well below the sub-cm requirement of OSIRIS.
                      Overall, the results of the commissioning successfully
                      prepared the ACU for nominal operation in OSIRIS. The
                      calibration of OSIRIS with the ACU was also the key aspect
                      of the software-focused part of the thesis. The presented
                      GEANT4-based energy calibration studies improved the
                      analysis algorithms in terms of stability and speed, while
                      also determining a minimal statistic of 30k events needed
                      for each of the involved radioactive isotopes to reach
                      required precision levels. The analyses of different source
                      capsule designs validated their usability in OSIRIS and led
                      to an approval for the calibration source production in late
                      2022. Also a first set of ACU calibration data, recorded
                      with the LED of the ACU, was analysed by the author. The
                      analysis focused on evaluating the overall detector
                      performance and identified irregularities for PMTs close to
                      the LED cable, promptly triggering investigations by the
                      OSIRIS group. The analysis also confirmed both the principle
                      of aligning the PMT timings and the expected detector
                      behaviour for different illumination levels.},
      keywords     = {Hochschulschrift (Other) / liquid scintillator detectors ;
                      neutrino physics ; hardware development ; software
                      development ; particle physics;
                      Flüssigszintintillatordetektoren ; Neutrinophysik ;
                      Hardwareentwicklung ; Softwareentwicklung ; Teilchenphysik ;
                      JUNO ; OSIRIS (Other)},
      cin          = {FFN},
      cid          = {I:(DE-Ds200)FFN-20210302OR452},
      pnm          = {612 - Cosmic Matter in the Laboratory (POF4-612)},
      pid          = {G:(DE-HGF)POF4-612},
      experiment   = {EXP:(DE-Ds200)JUNO-2022},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2025-02894},
      url          = {https://repository.gsi.de/record/362228},
}