Topological Track Reconstruction in Liquid Scintillator and LENA as a Far-Detector in an LBNO Experiment

Unsegmented liquid scintillator (LSc) neutrino detectors have proven to be successful instruments of neutrino physics. They usually measure terrestrial and astrophysical low-energy (LE) neutrinos and antineutrinos with energies up to some tens of MeV. Designs for next-generation detectors based on this technology intend to use several tens of kilotons of LSc. Two examples are the Low Energy Neutrino Astronomy (LENA) project with 50 kt considered in Europe and the Jiangmen Underground Neutrino Observatory (JUNO) with 20 kt already under construction in China. A key factor to reach the scientific goals of these projects, e.g., the determination of the neutrino mass ordering (MO) in the case of JUNO, will be the efficient rejection of background from radioisotopes produced by cosmogenic muons. This requires accurate reconstructions of extended muon event topologies in the LSc volume.The first part of this work is about the implementation of a novel, iterative track reconstruction procedure for unsegmented LSc detectors and a basic evaluation of its performance with the LENA detector simulation. The ultimate goal of the new method is to reconstruct the spatial number density distribution of optical photon emissions. This will give access to a charged particle's differential energy loss dE / dx in LSc and resolve details of an event's topology, e.g., induced particle showers. Visual comparisons of reconstruction outcomes with Monte Carlo (MC) truths already provide evidence for this capability. First quantitative results were extracted from the 3D reconstruction data of fully-contained muons in the kinetic energy range from 1 to 10 GeV: Despite some well understood systematic effects in the current method to find start and end point of a track, resolutions ≲ 25 cm lateral to the reconstructed track were ascertained for these spots. The determined angular resolution of ∼1.4° at 1 GeV improves to ∼0.3° with rising muon energy. With the current analysis method, the relative energy resolution approximately follows 10% / Sqrt(E / 1 GeV) + 2%.The application of the new technique is not the limited to cosmogenic muons. Future advancements may allow the reconstruction of the complex event topologies of GeV neutrino interactions. Beyond the (usual) LE neutrino program, this case would open up a new range of applications for unsegmented LSc detectors. The second part of this work therefore investigates the performance of LENA in a long-baseline neutrino oscillation (LBNO) experiment with a conventional multi-GeV neutrino beam as proposed in the Large Apparatus for Grand Unification and Neutrino Astrophysics (LAGUNA)-LBNO design study: A 750 kW neutrino beam aiming over a distance of ∼2300 km from the Conseil Européen pour laRecherche Nucléaire (CERN) to the Pyhäsalmi mine in central Finland. The potential to discover the neutrino MO and leptonic CP-violation was studied with the General Long Baseline Experiment Simulator (GLoBES) package in combination with MC techniques. Assuming ten years of runtime equally shared between neutrino and antineutrino mode, only a low sensitivity to CP-violation was found. However, in the MO study, the inverted ordering (IO) (normal ordering (NO)) hypothesis could be rejected at true NO (IO) with a median sensitivity of 4.6-6.7σ (4.2-5.8σ), depending on the true value of the CP-violating phase δ_CP