TY  - GEN
Y1  - 2017///
ID  - heidok22621
AV  - public
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/22621/
N2  - 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 10^26 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 T_1/2 > 5.3 * 10^25 yr at 90% C.L., with a median sensitivity of T_1/2 > 4.0 * 10^25 yr at 90%C.L.
TI  - Pulse Shape Analysis for the GERDA Experiment to Set a New Limit on the Half-life of Neutrinoless Double Beta Decay of Ge-76
A1  - Wagner, Victoria Elisabeth
ER  -