The GERmanium Detector Array

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6.4.2017          our recent results on 0νββ decay have been published by Nature:    doi:10.1038/nature21717

         Background free search for neutrinoless double-β decay with GERDA

         Nature 554 (201) 47-52    ( doi:10.1038/nature21717 )       and in    arxive 1703.00570

        our press releases:     english     german     at IDW     italian     russian

         comments in Nature 544, p. 38 by P. S. Barbeau

15.2.2017 histograms and data sets for analysis 2016 of GERDA Phase II

figure 1 figure 2 figure 3 figure 4
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01-Instrumentation_in_cryostat-Heisel.jpg  1: Lowering the germanium detector array into the liquid argon. View from top. © M. Heisel, GERDA collaboration  02-MuonVeto-Freund.jpg  2: The inner walls of the water tank are covered by a reflecting foil improving the light detection. This permits the identification of cosmic muons. © K. Freund, GERDA collaboration 
03-GERDA-3694-Suvorov.jpg  3: Working on the germanium detector array within the glove box which is located in the clean room on top of the liquid argon cryostat. © J. Suvorov, GERDA collaboration  06-View_bottom-up-Wagner.jpg  6: The fiber shroud of the liquid argon veto and the copper head for mounting the germanium strings. View from bottom. © V. Wagner, GERDA collaboration 
04-GERDA-3720-Suvorov.jpg  4: Attaching another string of germanium detectors to the array. © J. Suvorov, GERDA collaboration 05-GERDA-0094-Schwingenheuer.jpg  5: Assembly of a germanium detector string within the glove box. © B. Schwingenheuer, GERDA collaboration 

You are free to use the plots and/or data, however, we ask you to make proper reference to our publications. If you need additional information please contact the editorialboard .

8.7.2016 Presentation of Phase II results at the NEUTRINO2016 by M. Agostini
First results from GERDA Phase II

29.6.2016 Presentation of Phase II results at LNGS by B. Schwingenheuer
First data release GERDA Phase II

The most recent GERDA publications   (go down for full list, search and more)

Background-free search for neutrinoless double-β decay of 76Ge with GERDA
Nature 544 (2017) 47 (6 April 2017)
GERDA collaboration

Many extensions of the Standard Model of particle physics explain the dominance of matter over antimatter in our Universe by neutrinos being their own antiparticles. This would imply the existence of neutrinoless double-β decay,which is an extremely rare lepton-number-violating radioactive decay process whose detection requires the utmost background suppression. Among the programmes that aim to detect this decay, the GERDA Collaboration is searching for neutrinoless double-β decay of 76Ge by operating bare detectors, made of germanium with an enriched 76 Ge fraction, in liquid argon. After having completed Phase I of data taking, we have recently launched Phase II. Here we report that in GERDA Phase II we have achieved a background level of approximately 10-3 counts/(keV kg yr). This implies that the experiment is background-free, even when increasing the exposure up to design level. This is achieved by use of an active veto system, superior germanium detector energy resolution and improved background recognition of our new detectors. No signal of neutrinoless double-β decay was found when Phase I and Phase II data were combined, and we deduce a lower-limit half-life of 5.3•1025 years at the 90 per cent confidence level. Our half-life sensitivity of 4.0•1025 years is competitive with the best experiments that use a substantially larger isotope mass. The potential of an essentially background-free search for neutrinoless double-β decay will facilitate a larger germanium experiment with sensitivity levels that will bring us closer to clarifying whether neutrinos are their own antiparticle.

Limits on uranium and thorium bulk content in Gerda Phase I detectors
Astroparticle Physics 91 (2017) 15-21
GERDA collaboration

Internal contaminations of 238U, 235U and 232Th in the bulk of high purity germanium detectors are potential backgrounds for experiments searching for neutrinoless double beta decay of 76Ge. The data from Gerda Phase I have been analyzed for alpha events from the decay chain of these contaminations by looking for full decay chains and for time correlations between successive decays in the same detector. No candidate events for a full chain have been found. Upper limits on the activities in the range of a few nBq/kg for 226Ra, 227Ac and 228Th, the long-lived daughter nuclides of 238U, 235U and 232Th, respectively, have been derived. With these upper limits a background index in the energy region of interest from 226Ra and 228Th contamination is estimated which satisfies the prerequisites of a future ton scale germanium double beta decay experiment.

Search of Neutrinoless Double Beta Decay with the GERDA Experiment
Nucl. Part. Physics Procs. 273 -- 275 (2016) 1876
GERDA collaboration

The GERDA (GERmanium Detector Array) is an experiment for the search of neutrinoless double beta decay (0νββ) in 76Ge, located at Laboratori Nazionali del Gran Sasso of INFN (Italy). In the first phase of the experiment, a 90% confidence level (C.L.) sensitivity of 2.4 · 1025 yr on the 0&nu:ββ decay half-life was achieved with a 21.6 kg·yr exposure and an unprecedented background index in the region of interest of 1.0−2 counts/(keV·kg·yr). No excess of signal events was found, and an experimental lower limit on the half-life of 2.1 · 1025 yr (90% C.L.) was established. Correspondingly, the limit on the effective Majorana neutrino mass is mee < 0.2-0.4 eV, depending on the considered nuclear matrix element. The previous claim for evidence of a 0νββ decay signal is strongly disfavored, and the field of research is open again.

The performance of the Muon Veto of the GERDA experiment
EPJC 76 (2016)298
K. Freund, R. Falkenstein, P. Grabmayr, A. Hegai, J. Jochum, M. Knapp, B. Lubsandorzhiev, F. Ritter, C. Schmitt, A.-K. Schütz, I. Jitnikov, E. Shevchik, M. Shirchenko, D. Zinatulin

Low background experiments need a suppression of cosmogenically induced events. The GERDA experiment located at LNGS is searching for the 0νββ decay of 76Ge. It is equipped with an active muon veto the main part of which is a water Cherenkov veto with 66 PMTs in the water tank surrounding the GERDA cryostat. With this system 806 live days have been recorded, 491 days were combined muon-germanium data. A muon detection efficiency of εμd=(99.935±0.015)% was found in a Monte Carlo simulation for the muons depositing energy in the germanium detectors. By examining coincident muon-germanium events a rejection efficiency of εμr=(99.2+0.3-0.4)% was found. Without veto condition the muons by themselves would cause a background index of BIμ=(3.16±0.85)·10-3 cts/(keV·kg·year) at Qββ.

2νββ decay of 76Ge into excited states with GERDA Phase I
J. Phys. G: Nucl. Part. Phys. 42 (2015) 115201
GERDA collaboration

Two neutrino double beta decay of 76Ge to excited states of 76Se has been studied using data from Phase I of the GERDA experiment. An array composed of up to 14 germanium detectors including detectors that have been isotopically enriched in 76Ge was deployed in liquid argon. The analysis of various possible transitions to excited final states is based on coincidence events between pairs of detectors where a de-excitation γ ray is detected in one detector and the two electrons in the other. No signal has been observed and an event counting profile likelihood analysis has been used to determine Frequentist 90% C.L. bounds for three transitions: 0+g.s. - 21+: T1/2 > 1.6 x 1023 yr, 0+g.s. - 01+: T1/2 > 3.7 x 1023 yr and 0+g.s. - 22+: T1/2 > 2.3 x 1023 yr. These bounds are more than two orders of magnitude larger than those reported previously. Bayesian 90% credibility bounds were extracted and used to exclude several models for the 0+g.s. - 01+ transition.
   IOP labTalk  , IOP Image of the week ,  local copy    selected for high lights 2015 in section 'Nuclear and particle astrophysics'

    GERDA publications   (searchable)

    Conference talks & posters and seminars

    PhD theses and related work


    GERDA in CERNCourier:
         issue September 2013:   GERDA sets new limits on neutrinoless double beta decay
         issue March 2014:   Neutrinoless double beta decay (2nd contribution)

    NATURE article on GERDA:   ( Neutrino physics: Beta test; Vol 487 Issue 7406 News Feature )

    Proposal to LNGS (Sep 21, 2004) pdf (3.5 MB)

    Technical Proposal (March 2005, Version 0.1) pdf (1.8 MB)

    Letter of Intent (Mar 16, 2004) ps, pdf, gzipped ps, see also: hep-ex/0404039)

Note1: Due to the copy rights held by the publishers we list publications and conference proceedings only, if the DOI exists.
Note2: Please make sure to refer to the most recent documents. Proper reference and credit to the GERDA Collaboration should be made.

Last modified: 16.2.2017 go to top