Background free search for neutrinoless double beta decay with GERDA Phase II
Creators: name: Agostini, M.
name: Allardt, M.
name: Bakalyarov, A. M.
name: Balata, M.
name: Barabanov, I.
name: Baudis, L.
name: Bauer, C.
name: Bellotti, E.
name: Belogurov, S.
name: Belyaev, S. T.
name: Benato, G.
name: Bettini, A.
name: Bezrukov, L.
name: Bode, T.
name: Borowicz, D.
name: Brudanin, V.
name: Brugnera, R.
name: Caldwell, A.
name: Cattadori, C.
name: Chernogorov, A.
name: D'Andrea, V.
name: Demidova, E. V.
name: DiMarco, N.
name: diVacri, A.
name: Domula, A.
name: Doroshkevich, E.
name: Egorov, V.
name: Falkenstein, R.
name: Fedorova, O.
name: Freund, K.
name: Frodyma, N.
name: Gangapshev, A.
name: Garfagnini, A.
name: Gooch, C.
name: Grabmayr, P.
name: Gurentsov, V.
name: Gusev, K.
name: Hakenmüller, J.
name: Hegai, A.
name: Heisel, M.
name: Hemmer, S.
name: Hofmann, W.
name: Hult, M.
name: Inzhechik, L. V.
name: Csáthy, J. Janicskó
name: Jochum, J.
name: Junker, M.
name: Kazalov, V.
name: Kihm, T.
name: Kirpichnikov, I. V.
name: Kirsch, A.
name: Kish, A.
name: Klimenko, A.
name: Kneißl, R.
name: Knöpfle, K. T.
name: Kochetov, O.
name: Kornoukhov, V. N.
name: Kuzminov, V. V.
name: Laubenstein, M.
name: Lazzaro, A.
name: Lebedev, V. I.
name: Lehnert, B.
name: Liao, H. Y.
name: Lindner, M.
name: Lippi, I.
name: Lubashevskiy, A.
name: Lubsandorzhiev, B.
name: Lutter, G.
name: Macolino, C.
name: Majorovits, B.
name: Maneschg, W.
name: Medinaceli, E.
name: Miloradovic, M.
name: Mingazheva, R.
name: Misiaszek, M.
name: Moseev, P.
name: Nemchenok, I.
name: Palioselitis, D.
name: Panas, K.
name: Pandola, L.
name: Pelczar, K.
name: Pullia, A.
name: Riboldi, S.
name: Rumyantseva, N.
name: Sada, C.
name: Salamida, F.
name: Salathe, M.
name: Schmitt, C.
name: Schneider, B.
name: Schönert, S.
name: Schreiner, J.
name: Schulz, O.
name: Schütz, A. -K.
name: Schwingenheuer, B.
name: Selivanenko, O.
name: Shevchik, E.
name: Shirchenko, M.
name: Simgen, H.
name: Smolnikov, A.
name: Stanco, L.
name: Vanhoefer, L.
name: Vasenko, A. A.
name: Veresnikova, A.
name: von Sturm, K.
name: Wagner, V.
name: Walter, M.
name: Wegmann, A.
name: Wester, T.
name: Wiesinger, C.
name: Wojcik, M.
name: Yanovich, E.
name: Zhitnikov, I.
name: Zhukov, S. V.
name: Zinatulina, D.
name: Zuber, K.
name: Zuzel, G.
Publisher: name: arXiv
Year: 2017
Subjects: subject: Nuclear Experiment (nucl-ex)
subject: High Energy Physics - Experiment (hep-ex)
subject: Instrumentation and Detectors (physics.ins-det)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The Standard Model of particle physics cannot explain the dominance of matter over anti-matter in our Universe. In many model extensions this is a very natural consequence of neutrinos being their own anti-particles (Majorana particles) which implies that a lepton number violating radioactive decay named neutrinoless double beta ($0νββ$) decay should exist. The detection of this extremely rare hypothetical process requires utmost suppression of any kind of backgrounds. The GERDA collaboration searches for $0νββ$ decay of $^{76}$Ge ($^{76}\rm{Ge} \rightarrow\,^{76}\rm{Se} + 2e^-$) by operating bare detectors made from germanium with enriched $^{76}$Ge fraction in liquid argon. Here, we report on first data of GERDA Phase II. A background level of $\approx10^{-3}$ cts/(keV$\cdot$kg$\cdot$yr) has been achieved which is the world-best if weighted by the narrow energy-signal region of germanium detectors. Combining Phase I and II data we find no signal and deduce a new lower limit for the half-life of $5.3\cdot10^{25}$ yr at 90 % C.L. Our sensitivity of $4.0\cdot10^{25}$ yr is competitive with the one of experiments with significantly larger isotope mass. GERDA is the first $0νββ$ experiment that will be background-free up to its design exposure. This progress relies on a novel active veto system, the superior germanium detector energy resolution and the improved background recognition of our new detectors. The unique discovery potential of an essentially background-free search for $0νββ$ decay motivates a larger germanium experiment with higher sensitivity.
description: 14 pages, 9 figures, 1 table; ; data, figures and images available at http://www.mpi-hd.mpg/gerda/public