
Abstract
The GERDA experiment has been proposed in 2004 as a new 76Ge double-beta decay experiment at LNGS. GERDA has installed in Hall A of LNGS a facility where germanium detectors made out of isotopically enriched material are operated inside a cryogenic fluid shield. The setup has probed the neutrinoless double beta decay of 76Ge with a sensitivity of T1/2 > 10^25 yr at 90% confidence level. With respect to previous experiments based on Ge the background has been reduced by an order of magnitude to 10^-2 counts/(keV kg x yr) due to the new design, to selection of pure material and to the employment of pulse shape analysis. After an exposure of 21.6 kg x yr during a period 2011 to 2013 and a blind analysis no signal is observed and a lower limit is derived for the half life of neutrinoless double beta decay of 76Ge yielding T1/2 > 2.1 x 10^25 x yr (90% C.L.). The corresponding effective mass of the neutrino amounts to 0.2-0.4 eV in case the light neutrino exchange is the dominant process. The combination with selected results from previous experiments with 76Ge yields T1/2 > 3.0 x 10^25 x yr (90% C.L.). Presently, Phase II is in preparation with the main aim of further background reduction by installation of an active veto for the liquid argon. Thirty new detectors with a total mass of about 20 kg will be deployed additionally to those used in Phase I. These new detectors are of BEGe (Broad Energy Germanium) type which excels in pulse shape discrimination for additional background reduction. With an exposure of 100 kg x yr a sensitivity of about 10^26 x yr for the half life of neutrinoless double beta decay will be reached.
Description
Collaboration
M. Agostini o, M. Allardt d, A.M. Bakalyarov m, M. Balata a, I. Barabanov k, L. Baudis s, C. Bauer g, N. Becerici-Schmidt n, E. Bellotti h,i, S. Belogurov l,k , S.T. Belyaev m, G. Benato s, A. Bettini p,q, L. Bezrukov k, T. Bode o, D. Borowicz c,e, V. Brudanin e, R. Brugnera p,q, A. Caldwell n, C. Cattadori i, A. Chernogorov l, V. D’Andrea a, E.V. Demidova l, A. di Vacri a, A. Domula d, E. Doroshkevich k, V. Egorov e, R. Falkenstein r, O. Fedorova k, K. Freund r, N. Frodyma c, A. Gangapshev k,g, A. Garfagnini p,q, C. Gooch n, P. Grabmayr r, V. Gurentsov k, K. Gusev m,e,o, C. Hahne d, A. Hegai r, M. Heisel g, S. Hemmer p,q, G. Heusser g, W. Hofmann g, M. Hult f , L.V. Inzhechik k, L. Ioannucci a, J. Janicsko Csathy o, J. Jochum r, M. Junker a, V. Kazalov k, T. Kihm g, I.V. Kirpichnikov l, A. Kirsch g, A. Kish s, A. Klimenko g,e, K.T. Knoepfle g, O. Kochetov e, V.N. Kornoukhov l,k, V.V. Kuzminov k, M. Laubenstein a, A. Lazzaro o, V.I. Lebedev m, B. Lehnert d, H.Y. Liao n, M. Lindner g, I. Lippi q, A. Lubashevskiy g,e, B. Lubsandorzhiev k, G. Lutter f, C. Macolino a, B. Majorovits n, W. Maneschg g, G. Marissens f, E. Medinaceli p,q, M. Miloradovic s, M. Misiaszek c, P. Moseev k, I. Nemchenok e, S. Nisi a, D. Palioselitis n, K. Panas c, L. Pandola b, K. Pelczar c, A. Pullia j, M. Reissfelder g, S. Riboldi j, N. Rumyantseva e, C. Sada p,q, F. Salamida i, M. Salathe g, C. Schmitt r, B. Schneider d, J. Schreiner g, O. Schulz n, B. Schwingenheuer g, S. Schoenert o, A-K. Schutz r, H. Seitz n, O. Selivanenko k, E. Shevchik e, M. Shirchenko m,e, H. Simgen g, A. Smolnikov g, L. Stanco q, M. Stepaniuk g, H. Strecker g, L. Vanhoefer n, A.A. Vasenko l, A. Veresnikova k, K. von Sturm p,q, V. Wagner g, M. Walter s, A. Wegmann g, T. Wester d, C. Wiesinger o, H. Wilsenach d, M. Wojcik c, E. Yanovich k, I. Zhitnikov e, S.V. Zhukov m, D. Zinatulina e, K. Zuber d, G. Zuzel c.
a INFN Laboratori Nazionali del Gran Sasso and Gran Sasso Science Institute, Assergi, Italy
b INFN Laboratori Nazionali del Sud, Catania, Italy
c Institute of Physics, Jagiellonian University, Cracow, Poland
d Institut fuer Kern und Teilchenphysik, Technische Universitaat Dresden, Germany
e Joint Institute for Nuclear Research, Dubna, Russia
f Institute for Reference Materials and Measurements, Geel, Belgium
g Max-Planck-Institut fuer Kernphysik, Heidelberg, Germany
h Dipartimento di Fisica, Università Milano Bicocca, Italy
i INFN Milano Bicocca, Milano, Italy
j Dipartimento di Fisica, Universita` degli Studi di Milano e INFN Milano, Italy
k Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, Russia
l Institute for Theoretical and Experimental Physics, Moscow, Russia
m National Research Centre “Kurchatov Institute”, Moscow, Russia
n Max-Planck-Institut fuer Physik, Muenchen, Germany
o Physik Department and Excellence Cluster Universe, Technische Universitaat Muenchen, Germany
p Dipartimento di Fisica e Astronomia dell’Università di Padova, Italy
q INFN Padova, Italy
r Physikalisches Institut, Eberhard Karls Universitaat Tuebingen, Germany
s Physik Institut der Universitaat Zurich, Switzerland
Chair of collaboration board: R. Brugnera