@phdthesis{536c5948-672a-4fda-b09f-8531af934e7a,
  abstract     = {{This thesis contributes to the development of the proposed NNBAR experiment at the<br/>European Spallation Source (ESS), which aims to search for free neutron-antineutron oscillations with unprecedented experimental sensitivity. Achieving this goal requires both an intense beam of cold neutrons and a detector capable of reconstructing the pionic final state expected from antineutron annihilation on a carbon target.<br/><br/>The first part of the thesis concerns the proposed second neutron source at ESS. It focuses on the development of a high-intensity liquid-deuterium moderator below the spallation target, intended to maximise the cold-neutron intensity for NNBAR. My work included neutronic studies and optimisation of the moderator, and assessment of the impact of engineering constraints on its performance. The results show that the final moderator concept remains compatible with the targeted increase in NNBAR experimental sensitivity relative to the last search for free neutron oscillations at the Institut Laue-Langevin by a factor of ≈ 1000. Exploratory studies were also carried out for a possible ultra-cold neutron converter in the moderator cooling block.<br/><br/>The second part of the thesis concerns the development of a time projection chamber (TPC) for the future NNBAR annihilation detector, where the TPC will be responsible for tracking charged particles. A track-reconstruction and analysis framework was developed for the TPC prototype and applied to simulated data, cosmic-muon measurements and data from the proton-beam elastic-scattering experiment at the Cyclotron Centre Bronowice in Krakow, Poland. This enabled validation of the reconstruction procedure on both simulated and experimental data, including track fitting, residual studies and dE/dx analysis.<br/><br/>These studies support the development of two essential parts of the NNBAR experiment: the high-intensity cold neutron source and the TPC for the annihilation detector.}},
  author       = {{Rataj, Blahoslav}},
  isbn         = {{978-91-90202-08-1}},
  keywords     = {{neutron-antineutron oscillations; European spallation source; time projection chamber; NNBAR; cold-neutron source; ultra-cold neutron source; moderator; Fysicumarkivet A:2026:Rataj}},
  language     = {{eng}},
  month        = {{05}},
  publisher    = {{Media-Tryck, Lund University, Sweden}},
  school       = {{Lund University}},
  title        = {{Development of the NNBAR Experiment at the ESS : Design of the Second Neutron Source and Towards the Realisation of Time Projection Chamber}},
  url          = {{https://lup.lub.lu.se/search/files/248864270/Thesis_BR_LUCRIS.pdf}},
  year         = {{2026}},
}