h1

%0 Thesis
%A Schunck, Matthias
%T On the measurement of high-energetic neutrinos with the IceCube neutrino telescope and with acoustic detection methods
%C Aachen
%I Publikationsserver der RWTH Aachen University
%M RWTH-CONV-143029
%P IX, 149 S. : Ill., graph. Darst.
%D 2011
%Z Aachen, Techn. Hochsch., Diss., 2011
%X Neutrino astronomy is a new field of astroparticle physics that uses neutrino detectors to observe astrophysical objects. Over the last few decades, several dedicated neutrino telescopes have been built and several other are planned for the near future. In this thesis, two subjects have been addressed to enhance the detection of astrophysical neutrinos with the existing IceCube neutrino telescope as well as to explore new detection methods, namely the acoustic detection. In the first part of this thesis, the determination of the acoustic attenuation length in South-Pole ice is presented. This is part of a feasibility study to investigate the acoustic neutrino detection as a possibility to enhance the detection of the highest-energy neutrinos. For this, the acoustic properties of the ice have to be known, and the South-Pole Acoustic Test Setup (SPATS) has been built to determine these. The attenuation length is determined using in-situ measurements with SPATS and a retrievable transmitter (pinger), which was deployed in a depth between 190 and 500m into the water-filled drilling holes. The setup of these measurements allowed for a data sample with few systematic effects. Even though, the unknown angular-dependent sensitivities of the SPATS sensor channels cannot be avoided and are considered as the dominant systematic effect for these measurements. In this thesis, the acoustic attenuation length is calculated by comparing the energy contents of the pinger pulses recorded by the various SPATS sensor channels for different distances between the pinger and the respective channel. The energy was calculated from the Fourier spectra of the pinger pulses for a frequency range between 5 and 35 kHz. The attenuation coefficient is calculated for each channel individually and the weighted mean over the distribution of all considered channels leads to an attenuation length of 264(+52 -37)m. The dependence of the attenuation on both depth and frequency has been investigated, showing no indications for either. This result is consistent with complementary analyses, using either the same or different data samples and analyses techniques. However, the measured value is an order of magnitude smaller than the theoretical prediction. For the acoustic neutrino detection at South Pole, this leads to the following implications. First, it is necessary to understand the mechanism of the acoustic attenuation in order to decide whether acoustic neutrino detection is feasible at South-Pole. The disagreement between the measurements and the theoretical prediction indicate that some of the assumptions leading to the predicted value have to be revised. Secondly, the attenuation length affects the design of a future acoustic detector at South Pole. Using the new information, a much denser spacing is required to achieve the same detection threshold as compared to the initial assumptions. The current effort of the SPATS collaborators is therefore to evaluate the feasibility of the acoustic detection under the new premise. In the second part, a new event reconstruction method based on a Top-Down approach is presented. The method has been implemented for the IC40 detector and applied to the muon energy reconstruction. The Top-Down method is based on the direct comparison of single measured events with a large sample of simulated (Monte-Carlo) events. Using a maximum-likelihood description, the Monte-Carlo event from this sample which has the maximum likelihood value, gives an estimate for the properties of the measured event. The Monte-Carlo events required for the comparison are stored in a database, containing the full event information from the simulations. For each measured event, a sample of Monte-Carlo events with a similar track geometry is selected from this database and compared with the measured event. An advantage of the Top-Down method is that it follows a forward-folding concept, incorporating all properties of the IceCube detector, such as its finite resolution and the ice properties, through the Monte-Carlo simulations. For the purpose of this study, a set of simple detector-level observables has been defined and tested. This likelihood description can be easily extended or replaced to include additional observables. A disadvantage of the method is that it relies on large numbers of Monte-Carlo events and is more computationally intensive than conventional reconstruction methods. Consequently, it is intended for the reconstruction of samples of interesting events, rather than a standard reconstruction procedure for all events. A proof of concept study using Monte-Carlo data has been performed to investigate the applicability of the Top-Down method to the muon energy reconstruction in IceCube. The Top-Down method has been demonstrated to work well and the results from this study can be used to further develop the Top-Down concept and to improve the reconstruction resolution as well as the general performance of the algorithm.
%K Elementarteilchenphysik (SWD)
%K Astrophysik (SWD)
%K Neutrino (SWD)
%K Experimentalphysik (SWD)
%K Antarktis (SWD)
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%U https://publications.rwth-aachen.de/record/82642