95.55.Vj Neutrino, muon, pion, and other elementary particle detectors; cosmic ray detectors (see also 29.40.-n Radiation detectors-in Nuclear physics)
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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.
Studies on the Selection of Neutrino-like Signals for the Acoustic Detection Test Device AMADEUS
(2013)
Acoustic neutrino detection is a promising approach for large-scale ultra-high energy neutrino detectors in water. According to the thermo-acoustic model, a acoustic pressure pulse is produced by a particle cascade that evolves when a UHE neutrino interacts in a medium like water or ice. The AMADEUS system was build to research the feasibility of this detection method. The system consists of an array of 36 acoustic sensors arranged in six clusters distributed over the ANTARES neutrino telescope on different length scales. The ANTARES detector, of which AMADEUS is a subsystem, is located in the Mediterranean Sea, 40 km off the coast of Toulon, southern France in a depth of about 2500m. In this work, a Monte Carlo simulation chain for acoustic neutrino detection devices in water is presented. The simulation chain covers the generation of the acoustic pulse produced by a neutrino interaction and its propagation to the sensors within the detector. Currently, ambient and transient noise models for the Mediterranean Sea and simulations of the data acquisition hardware, equivalent to the one used in ANTARES/AMADEUS, are implemented. A pre-selection scheme for neutrino-like signals based on matched filtering is employed, as it is used for on-line filtering. To simulate the whole processing chain for experimental data, signal classification and acoustic source reconstruction algorithms are integrated in an analysis chain. An overview of design and capabilities of the simulation and analysis chain are presented and the results of the studies are discussed, including the analysis of the transient background as measured at the AMADEUS site and the calculation of an effective volume and a transient-free, limit-setting potential of the AMADEUS detector.
Built in the deep sea of the Mediterranean near Toulon, France, the ANTARES neutrino telescope detects neutrinos which interact inside or close to the detector and bring forth a muon which emits Cherenkov light. The detector consists of a photomultiplier array mounted on flexible strings which are anchored on the seabed. From the position and time of the incident Cherenkov photons, the direction of the muon track and thereby that of its precursor neutrino are reconstructed. Part of the project’s physics program is to search indirectly for Dark Matter, by looking for neutrinos emitted in annihilation processes predicted by theories describing the yet unidentified Dark Matter particles. This thesis covers several aspects of searching for neutrinos from the annihilation of Dark Matter accumulating in the centres of the Earth and the Sun. Introductory, the evidences for the existence of Dark Matter are reviewed and the theoretical foundation of Dark Matter candidate particles are explained, before presenting the different methods of direct and indirect Dark Matter search and examining their prospects. Furthermore, an overview of theANTARESdetector is given, with focus on data acquisition and alignment. The sensitivity of ANTARES to the neutrinos from Dark Matter annihilation in the Sun predicted by the theory of minimal Supergravity (mSugra) is studied, finding that with five years of data parts of the mSugra parameter space could be excluded. The neutrino reconstruction procedures applied in analysing the neutrino flux from the direction of the Earth’s centre are introduced, highlighting the development of an efficient hit selection procedure and a dedicated low energy reconstruction algorithm. An improved Monte Carlo simulation of the atmospheric neutrinos and muons, which includes in situ measured optical background and photomultiplier gain distributions, is used to calculate the expected background for the analysis. With these reconstruction and simulation methods an upper limit on the rate of Dark Matter annihilation inside Earth from the data taken in December 2010 is obtained, and the corresponding sensitivity of ANTARES for five years is calculated.
The KM3NeT-project is a common european effort for the Design and construction of a deep-sea neutrino telescope in the Mediterranean. In this phd-thesis the results of simulations for the KM3NeT Design Study are presented. Many different possible photodetection-layouts and detector geometries have been simulated and analysed. Additionally, the physics potential of the most promising configurations was studied.