8 research outputs found
Search for double beta decay with HPGe detectors at the Gran Sasso underground laboratory
Neutrinoless double-beta (0νββ) decay is practically the only way to establish the Majorana nature of the neutrino mass and its decay rate provides a probe of an effective neutrino mass. Double beta experiments are long-running underground experiments with specific challenges concerning the background reduction and the long term stability. These problems are addressed in this work for the Heidelberg-Moscow, Genius-Test-Facility and Gerda experiments. The Heidelberg-Moscow (HdM) experiment collected data with enriched 76Ge detectors from 1990 to 2003. An improved analysis of Heidelberg-Moscow data is presented, exploiting new calibration and spectral shape measurements with the HdM detectors. Genius-Test-Facility was a test-facility that verified the feasibility of using bare germanium detectors in liquid nitrogen. The first year results of this experiment are discussed. The Gerda experiment has been designed to further increase the sensitivity by operating bare germanium detectors in a high purity cryogenic liquid, which simultaneously serves as a shielding against background and as a cooling media. In the preparatory stage of Gerda, an external background gamma flux measurement was done at the experimental site in the Hall A of the Gran Sasso laboratory. The characterization of the enriched detectors from the Heidelberg-Moscow and Igex experiments was performed in the underground detector laboratory for the Gerda collaboration. Long term stability measurements of a bare HPGe detector in liquid argon were carried out. Based on these measurements, the first lower limit on the half-life of neutrinoless double electron capture of 36Ar was established to be 1.85·10^18 y (68% C.L)
Pulse shape discrimination studies with a Broad-Energy Germanium detector for signal identification and background suppression in the GERDA double beta decay experiment
First studies of event discrimination with a Broad-Energy Germanium (BEGe)
detector are presented. A novel pulse shape method, exploiting the
characteristic electrical field distribution inside BEGe detectors, allows to
identify efficiently single-site events and to reject multi-site events. The
first are typical for neutrinoless double beta decays (0-nu-2-beta) and the
latter for backgrounds from gamma-ray interactions. The obtained survival
probabilities of backgrounds at energies close to Q(76Ge) = 2039 keV are 0.93%
for events from 60Co, 21% from 226Ra and 40% from 228Th. This background
suppression is achieved with 89% acceptance of 228Th double escape events,
which are dominated by single site interactions. Approximately equal acceptance
is expected for 0-nu-2-beta-decay events. Collimated beam and Compton
coincidence measurements demonstrate that the discrimination is largely
independent of the interaction location inside the crystal and validate the
pulse-shape cut in the energy range of Q(76Ge). The application of BEGe
detectors in the GERDA and the Majorana double beta decay experiments is under
study.Comment: 22 pages, 16 figures, submitted to JINST: JINST_018P_080
Pulse shape discrimination studies with a Broad-Energy Germanium detector for signal identification and background suppression in the GERDA double beta decay experiment
First studies of event discrimination with a Broad-Energy Germanium (BEGe)
detector are presented. A novel pulse shape method, exploiting the
characteristic electrical field distribution inside BEGe detectors, allows to
identify efficiently single-site events and to reject multi-site events. The
first are typical for neutrinoless double beta decays (0-nu-2-beta) and the
latter for backgrounds from gamma-ray interactions. The obtained survival
probabilities of backgrounds at energies close to Q(76Ge) = 2039 keV are 0.93%
for events from 60Co, 21% from 226Ra and 40% from 228Th. This background
suppression is achieved with 89% acceptance of 228Th double escape events,
which are dominated by single site interactions. Approximately equal acceptance
is expected for 0-nu-2-beta-decay events. Collimated beam and Compton
coincidence measurements demonstrate that the discrimination is largely
independent of the interaction location inside the crystal and validate the
pulse-shape cut in the energy range of Q(76Ge). The application of BEGe
detectors in the GERDA and the Majorana double beta decay experiments is under
study.Comment: 22 pages, 16 figures, submitted to JINST: JINST_018P_080
Pulse shape discrimination studies with a Broad-Energy Germanium detector for signal identification and background suppression in the GERDA double beta decay experiment
First studies of event discrimination with a Broad-Energy Germanium (BEGe)
detector are presented. A novel pulse shape method, exploiting the
characteristic electrical field distribution inside BEGe detectors, allows to
identify efficiently single-site events and to reject multi-site events. The
first are typical for neutrinoless double beta decays (0-nu-2-beta) and the
latter for backgrounds from gamma-ray interactions. The obtained survival
probabilities of backgrounds at energies close to Q(76Ge) = 2039 keV are 0.93%
for events from 60Co, 21% from 226Ra and 40% from 228Th. This background
suppression is achieved with 89% acceptance of 228Th double escape events,
which are dominated by single site interactions. Approximately equal acceptance
is expected for 0-nu-2-beta-decay events. Collimated beam and Compton
coincidence measurements demonstrate that the discrimination is largely
independent of the interaction location inside the crystal and validate the
pulse-shape cut in the energy range of Q(76Ge). The application of BEGe
detectors in the GERDA and the Majorana double beta decay experiments is under
study.Comment: 22 pages, 16 figures, submitted to JINST: JINST_018P_080