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Title: Status of the GERDA Phase II upgrade

Abstract

The GERDA experiment is designed to search for neutrinoless double beta (0νββ) decay of {sup 76}Ge. In Phase I of the experiment a background index of 10{sup −2} cts/(keV·kg·yr) was reached. A lower limit on the half-life of the 0νββ decay of {sup 76}Ge was set to 2.1·10{sup 25} yr (at 90% C.L.). The aim of Phase II is to reach a sensitivity of the half-life of about 10{sup 26} yr. To increase the exposure thirty new Broad Energy Germanium (BEGe) detectors have been produced. These detectors are distinct for their improved energy resolution and enhanced pulse shape discrimination of signal from background events. Further background reduction will be reached by a light instrumentation to read out argon scintillation light. In April 2015 the light instrumentation together with eight BEGe detectors has been successfully deployed in the GERDA cryostat. In a commissioning run it was shown that two of the major background components, external γ-rays from {sup 214}Bi and {sup 208}Tl decays, were suppressed up to two orders of magnitude. We are confident to reach a background index of 10{sup −3} cts/(keV·kg·yr) which is the design goal for GERDA Phase II.

Authors:
 [1]
  1. Max-Planck-Insitut für Kernphysik, Heidelberg (Germany)
Publication Date:
OSTI Identifier:
22609101
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1743; Journal Issue: 1; Conference: CETUP 2015: Workshop on dark matter, neutrino physics and astrophysics, Deadwood, SD (United States), 15 Jun - 17 Jul 2015, PPC 2015: 9. international conference on interconnections between particle physics and cosmology, Deadwood, SD (United States), 15 Jun - 17 Jul 2015; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ARGON; BISMUTH 214; COMMISSIONING; CRYOSTATS; ENERGY RESOLUTION; GAMMA DECAY; GAMMA RADIATION; GE SEMICONDUCTOR DETECTORS; GERMANIUM 76; HALF-LIFE; NEUTRINOLESS DOUBLE BETA DECAY; READOUT SYSTEMS; SCINTILLATIONS; SENSITIVITY; THALLIUM 208

Citation Formats

Wagner, Victoria. Status of the GERDA Phase II upgrade. United States: N. p., 2016. Web. doi:10.1063/1.4953322.
Wagner, Victoria. Status of the GERDA Phase II upgrade. United States. doi:10.1063/1.4953322.
Wagner, Victoria. 2016. "Status of the GERDA Phase II upgrade". United States. doi:10.1063/1.4953322.
@article{osti_22609101,
title = {Status of the GERDA Phase II upgrade},
author = {Wagner, Victoria},
abstractNote = {The GERDA experiment is designed to search for neutrinoless double beta (0νββ) decay of {sup 76}Ge. In Phase I of the experiment a background index of 10{sup −2} cts/(keV·kg·yr) was reached. A lower limit on the half-life of the 0νββ decay of {sup 76}Ge was set to 2.1·10{sup 25} yr (at 90% C.L.). The aim of Phase II is to reach a sensitivity of the half-life of about 10{sup 26} yr. To increase the exposure thirty new Broad Energy Germanium (BEGe) detectors have been produced. These detectors are distinct for their improved energy resolution and enhanced pulse shape discrimination of signal from background events. Further background reduction will be reached by a light instrumentation to read out argon scintillation light. In April 2015 the light instrumentation together with eight BEGe detectors has been successfully deployed in the GERDA cryostat. In a commissioning run it was shown that two of the major background components, external γ-rays from {sup 214}Bi and {sup 208}Tl decays, were suppressed up to two orders of magnitude. We are confident to reach a background index of 10{sup −3} cts/(keV·kg·yr) which is the design goal for GERDA Phase II.},
doi = {10.1063/1.4953322},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1743,
place = {United States},
year = 2016,
month = 6
}
  • A search for neutrinoless ββ decay processes accompanied with Majoron emission has been performed using data collected during Phase I of the GERmanium Detector Array (GERDA) experiment at the Laboratori Nazionali del Gran Sasso of INFN (Italy). Processes with spectral indices n = 1,2,3,7 were searched for. No signals were found and lower limits of the order of 10 23 yr on their half-lives were derived, yielding substantially improved results compared to previous experiments with 76Ge. A new result for the half-life of the neutrino-accompanied ββ decay of 76Ge with significantly reduced uncertainties is also given, resulting in T more » 1/2 = (1.926 ± 0.094) × 10 21 yr.« less
  • The Germanium Detector Array (GERDA) in the search for neutrinoless {beta}{beta} decays of {sup 76}Ge at LNGS will operate bare germanium diodes enriched in {sup 76}Ge in an (optional active) cryogenic fluid shield to investigate neutrinoless {beta}{beta} decay with a sensitivity of T{sub 1/2} > 2 x 10{sup 26} yr after an exposure of 100 kg yr. Recent progress includes the installation of the first underground infrastructures at Gran Sasso, the completion of the enrichment of 37.5 kg of germanium material for detector construction, prototyping of low-mass detector support and contacts, and front-end and DAQ electronics, as well as themore » preparation for construction of the cryogenic vessel and water tank.« less
  • The GERDA experiment located at the Laboratori Nazionali del Gran Sasso of INFN searches for neutrinoless double beta (0νββ) decay of 76Ge using germanium diodes as source and detector. In Phase I of the experiment eight semi-coaxial and five BEGe type detectors have been deployed. The latter type is used in this field of research for the first time. All detectors are made from material with enriched 76Ge fraction. The experimental sensitivity can be improved by analyzing the pulse shape of the detector signals with the aim to reject background events. This paper documents the algorithms developed before the datamore » of Phase I were unblinded. The double escape peak (DEP) and Compton edge events of 2.615 MeV γ rays from 208Tl decays as well as two-neutrino double beta (2νββ) decays of 76Ge are used as proxies for 0νββ decay. For BEGe detectors the chosen selection is based on a single pulse shape parameter. It accepts 0.92 ± 0.02 of signal-like events while about 80 % of the background events at Qββ = 2039 keV are rejected. For semi-coaxial detectors three analyses are developed. The one based on an artificial neural network is used for the search of 0νββ decay. It retains 90 % of DEP events and rejects about half of the events around Qββ . The 2νββ events have an efficiency of 0.85±0.02 and the one for 0νββ decays is estimated to be 0.90 +0.05 -0.09 . A second analysis uses a likelihood approach trained on Compton edge events. The third approach uses two pulse shape parameters. The latter two methods confirm the classification of the neural network since about 90 % of the data events rejected by the neural network are also removed by both of them. In general, the selection efficiency extracted from DEP events agrees well with those determined from Compton edge events or from 2νββ decays.« less
  • An optimized digital shaping filter has been developed for the Gerda experiment which searches for neutrinoless double beta decay inmore » $$^{76}$$Ge. The Gerda Phase I energy calibration data have been reprocessed and an average improvement of 0.3 keV in energy resolution (FWHM) corresponding to 10% at the $Q$ value for $$0\nu \beta \beta $$0νββ decay in $$^{76}$$Ge is obtained. This is possible thanks to the enhanced low-frequency noise rejection of this Zero Area Cusp (ZAC) signal shaping filter.« less
  • Neutrinoless double electron capture is a process that, if detected, would give evidence of lepton number violation and the Majorana nature of neutrinos. Here, a search for neutrinoless double electron capture of 36Ar has been performed with germanium detectors installed in liquid argon using data from Phase I of the GERmanium Detector Array (Gerda) experiment at the Gran Sasso Laboratory of INFN, Italy. No signal was observed and an experimental lower limit on the half-life of the radiative neutrinoless double electron capture of 36 Ar was established: T 1/2 > 3.6 × 10 21 years at 90% CI.