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Universität Heidelberg

1. Wagner, Victoria Elisabeth. Pulse Shape Analysis for the GERDA Experiment to Set a New Limit on the Half-life of Neutrinoless Double Beta Decay of Ge-76.

Degree: PhD, The Faculty of Physics and Astronomy, 2017, Universität Heidelberg

The GERDA experiment searches for neutrinoless double beta (0nbb) decay of Ge-76 using high purity germanium (HPGe) detectors operated in liquid argon (LAr). The aim is to explore half-lives of the order of 1026 yr. Therefore, GERDA relies on improved active background reduction techniques such as pulse shape discrimination (PSD) in which the time structure of the germanium signals is analyzed to discriminate signal- from background-like events. Two types of HPGe detectors are operated: semi-coaxial detectors previously used in the Heidelberg-Moscow and IGEX experiments and new Broad Energy Germanium (BEGe) detectors which feature an improved energy resolution and enhanced PSD. In Phase I of the experiment, five enriched BEGe detectors were used for the first time in the search for 0nbb decay. A PSD based on a single parameter, the ratio of the maximum current amplitude over the energy A/E is applied. 83% of the background events in a 232 keV region around Qbb are rejected with a high signal efficiency of (92.1 +/- 1.9) %. The achieved background index (BI) is (5.4 +4.1 -3.4) * 10-3 counts/(keV*kg*yr). This is an improvement by a factor of 10 compared to previous germanium based 0nbb experiments. Phase II of the experiment includes a major upgrade: for further background rejection, the LAr cryostat is instrumented to detect argon scintillation light. Additional 25 BEGe detectors are installed. After PSD and LAr veto a BI of (0.7 +1.3 -0.5) * 10-3 counts/(keV*kg*yr) is achieved. This is the best BI achieved in 0nbb experiments so far. A frequentist statistical analysis is performed on the combined data collected in GERDA Phase I and the first Phase II release. A new limit on the half-life of 0nbb decay of Ge-76 is set to T1/2 > 5.3 * 1025 yr at 90% C.L., with a median sensitivity of T1/2 > 4.0 * 1025 yr at 90%C.L. Advisors/Committee Members: Lindner, Manfred (advisor).

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Wagner, V. E. (2017). Pulse Shape Analysis for the GERDA Experiment to Set a New Limit on the Half-life of Neutrinoless Double Beta Decay of Ge-76. (Doctoral Dissertation). Universität Heidelberg. Retrieved from http://www.ub.uni-heidelberg.de/archiv/22621; 10.11588/heidok.00022621

Chicago Manual of Style (16th Edition):

Wagner, Victoria Elisabeth. “Pulse Shape Analysis for the GERDA Experiment to Set a New Limit on the Half-life of Neutrinoless Double Beta Decay of Ge-76.” 2017. Doctoral Dissertation, Universität Heidelberg. Accessed August 22, 2017. http://www.ub.uni-heidelberg.de/archiv/22621; 10.11588/heidok.00022621.

MLA Handbook (7th Edition):

Wagner, Victoria Elisabeth. “Pulse Shape Analysis for the GERDA Experiment to Set a New Limit on the Half-life of Neutrinoless Double Beta Decay of Ge-76.” 2017. Web. 22 Aug 2017.

Vancouver:

Wagner VE. Pulse Shape Analysis for the GERDA Experiment to Set a New Limit on the Half-life of Neutrinoless Double Beta Decay of Ge-76. [Internet] [Doctoral dissertation]. Universität Heidelberg; 2017. [cited 2017 Aug 22]. Available from: http://www.ub.uni-heidelberg.de/archiv/22621; 10.11588/heidok.00022621.

Council of Science Editors:

Wagner VE. Pulse Shape Analysis for the GERDA Experiment to Set a New Limit on the Half-life of Neutrinoless Double Beta Decay of Ge-76. [Doctoral Dissertation]. Universität Heidelberg; 2017. Available from: http://www.ub.uni-heidelberg.de/archiv/22621; 10.11588/heidok.00022621

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