Measuring the neutrino mass hierarchy with the future KM3NeT/ORCA detector

• Main Author: Hofestädt, Jannik
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2017
• Subjects: Neutrinooszillation; Neutrinonachweis; Neutrinodetektor; Machbarkeitsstudie; ddc:539; Orca
• Online Access: https://opus4.kobv.de/opus4-fau/frontdoor/index/index/docId/8277; https://nbn-resolving.org/urn:nbn:de:bvb:29-opus4-82770; https://opus4.kobv.de/opus4-fau/files/8277/Dissertation_JHofestaedt.pdf

The neutrino mass hierarchy can be determined by measuring the energy- and zenith-angle-dependent oscillation pattern of few-GeV atmospheric neutrinos that have traversed the Earth. This measurement is the main science goal of KM3NeT/ORCA (`Oscillation Research with Cosmics in the Abyss'), a planned multi-megaton underwater Cherenkov detector in the Mediterranean Sea. A key task is the reconstruction of shower-like events induced by electron neutrinos in charged-current interactions, which substantially affect the neutrino mass hierarchy sensitivity. In this thesis, numerous aspects of the expected neutrino detection performance of the planned ORCA detector are investigated. A new reconstruction algorithm for neutrino-induced shower-like events is developed. The achieved resolutions are close to the reconstruction accuracy limits imposed by intrinsic fluctuations in the Cherenkov light signatures. These intrinsic resolution limits are derived as part of this thesis. Differences in event reconstruction capabilities between water- and ice-based Cherenkov detectors are discussed. The configuration of existing trigger algorithms is optimised for the ORCA detector. Based on the developed shower reconstruction, a detector optimisation study of the photosensor density is performed. In addition, it is shown that optical background noise in the deep Mediterranean Sea is not expected to compromise the feasibility of the neutrino mass hierarchy measurement with ORCA. Together, these investigations contribute significantly to the estimated neutrino mass hierarchy sensitivity of ORCA published in the 'Letter of Intent' for KM3NeT, illustrate why a new optimised detector geometry is proposed, and give pointers as to how to improve the neutrino detection performance and consequently the neutrino mass hierarchy sensitivity of ORCA. Die Neutrinomassenhierachie lässt sich durch die Vermessung der energie- und zenitwinkelabhängigen Oszillationswahrscheinlichkeiten von atmosphärischen Neutrinos im Energiebereich von einigen GeV ...