4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014;
Waikoloa, Hawaii
Session 1WM: Neutrinoless Double Beta Decay Experiments and Underground Physics Challenges I
9:00 AM–12:30 PM,
Tuesday, October 7, 2014
Room: Kona 5
Chair: Kevin Lesko, Lawrence Berkeley National Laboratory
Abstract ID: BAPS.2014.HAW.1WM.3
Abstract: 1WM.00003 : Upgrades for GERDA Phase II
10:00 AM–10:30 AM
Preview Abstract
Abstract
Author:
Mark Heisel
(Max Planck Institute for Nuclear Physics)
The Germanium Detector Array (GERDA) experiment is searching for the neutrinoless double beta decay ($0\nu\beta\beta$) of $^{76}$Ge. It is a process that violates lepton number conservation and is predicted to occur in extensions of the standard model of particle physics. GERDA is located underground in the Gran Sasso National Laboratory (LNGS), Italy. An array of bare high-purity germanium detectors enriched in $^{76}$Ge is operated in a cryostat with 64 m$^3$ of liquid argon supplemented by a 3 m thick shield of water. The experiment aims at exploring the $0\nu\beta\beta$ decay up to a half life of $2\cdot10^{26}$ yr in two phases:
Phase I of the experiment has been concluded last year. No signal is observed and the so far best limit is derived for the half life of the $0\nu\beta\beta$ decay of $^{76}$Ge, $T_{1/2}^{0\nu}\leq2.1\cdot10^{25}$ yr (90\% C.L.), after an exposure of $21.6 $kg$\cdot$yr. The result refutes an earlier claim of discovery with high probability. The background index of $1\cdot10^{-2}$ cts/(keV$\cdot$kg$\cdot$yr) is lower by about one order of magnitude compared to previous experiments.
At present the experiment is being upgraded to Phase II. The aim is to collect an exposure of $100 $kg$\cdot$yr and further reduce the background by another order of magnitude to a level of $\leq10^{-3}$ cts/(keV$\cdot$kg$\cdot$yr). The detector mass will be increased by $\sim$20 kg of new Broad Energy Germanium (BEGe) detectors from enriched $^{76}$Ge, which exhibit superior pulse shape discrimination and hence background rejection power. Low mass detector holders, cold front-end electronics, contacting and cabling schemes are redesigned for ultra low mass and radiopurity. In addition, a retractable liquid argon veto will be installed to efficiently suppress background events that induce scintillation in the liquid argon. A hybrid solution of photomultiplier tubes and silicon photomultipliers coupled to scintillating fibres was chosen. This talk gives an account of the results and these challenging modifications to meet our design goals.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.HAW.1WM.3