/ nucl-ex arXiv:1703.00570


Background free search for neutrinoless double beta decay with GERDA Phase II


Agostini, M. (Gran Sasso) ; Allardt, M. (Dresden, Tech. U.) ; Bakalyarov, A.M. (Kurchatov Inst., Moscow) ; Balata, M. (Gran Sasso) ; Barabanov, I. (Moscow, INR) ; Baudis, L. (Zurich U.) ; Bauer, C. (Heidelberg, Max Planck Inst.) ; Bellotti, E. (INFN, Milan Bicocca) ; Belogurov, S. (Moscow, ITEP) ; Belyaev, S.T. (Kurchatov Inst., Moscow) ; Benato, G. (Zurich U.) ; Bettini, A. (INFN, Padua) ; Bezrukov, L. (Moscow, INR) ; Bode, T. (Munich, Tech. U., Universe) ; Borowicz, D. (Dubna, JINR) ; Brudanin, V. (Dubna, JINR) ; Brugnera, R. (INFN, Padua) ; Caldwell, A. (Munich, Max Planck Inst.) ; Cattadori, C. (INFN, Milan Bicocca) ; Chernogorov, A. (Moscow, ITEP) ; D'Andrea, V. (Dresden, Tech. U.) ; Demidova, E.V. (Moscow, ITEP) ; Di Marco, N. (Gran Sasso) ; di Vacri, A. (Gran Sasso) ; Domula, A. (Dresden, Tech. U.) ; Doroshkevich, E. (Moscow, INR) ; Egorov, V. (Dubna, JINR) ; Falkenstein, R. (Tubingen U.) ; Fedorova, O. (Moscow, INR) ; Freund, K. (Tubingen U.) ; Frodyma, N. (Jagiellonian U.) ; Gangapshev, A. (Moscow, INR) ; Garfagnini, A. (INFN, Padua) ; Gooch, C. (Munich, Max Planck Inst.) ; Grabmayr, P. (Tubingen U.) ; Gurentsov, V. (Moscow, INR) ; Gusev, K. (Munich, Tech. U., Universe) ; Hakenmüller, J. (Heidelberg, Max Planck Inst.) ; Hegai, A. (Tubingen U.) ; Heisel, M. (Heidelberg, Max Planck Inst.) ; Hemmer, S. (INFN, Padua) ; Hofmann, W. (Heidelberg, Max Planck Inst.) ; Hult, M. (Geel, JRC) ; Inzhechik, L.V. (Moscow, INR) ; Janicskó Csáthy, J. (Munich, Tech. U., Universe) ; Jochum, J. (Tubingen U.) ; Junker, M. (Gran Sasso) ; Kazalov, V. (Moscow, INR) ; Kihm, T. (Heidelberg, Max Planck Inst.) ; Kirpichnikov, I.V. (Moscow, ITEP) ; Kirsch, A. (Heidelberg, Max Planck Inst.) ; Kish, A. (Zurich U.) ; Klimenko, A. (Heidelberg, Max Planck Inst.) ; Kneißl, R. (Munich, Max Planck Inst.) ; Knöpfle, K.T. (Heidelberg, Max Planck Inst.) ; Kochetov, O. (Dubna, JINR) ; Kornoukhov, V.N. (Moscow, ITEP) ; Kuzminov, V.V. (Moscow, INR) ; Laubenstein, M. (Gran Sasso) ; Lazzaro, A. (Munich, Tech. U., Universe) ; Lebedev, V.I. (Kurchatov Inst., Moscow) ; Lehnert, B. (Dresden, Tech. U.) ; Liao, H.Y. (Munich, Max Planck Inst.) ; Lindner, M. (Heidelberg, Max Planck Inst.) ; Lippi, I. (INFN, Padua) ; Lubashevskiy, A. (Heidelberg, Max Planck Inst.) ; Lubsandorzhiev, B. (Moscow, INR) ; Lutter, G. (Geel, JRC) ; Macolino, C. (Gran Sasso) ; Misiaszek, M. (Jagiellonian U.) ; Moseev, P. (Moscow, INR) ; Nemchenok, I. (Dubna, JINR) ; Palioselitis, D. (Munich, Max Planck Inst.) ; Panas, K. (Jagiellonian U.) ; Pandola, L. (INFN, LNS) ; Pelczar, K. (Jagiellonian U.) ; Pullia, A. (Milan U.) ; Riboldi, S. (Milan U.) ; Rumyantseva, N. (Dubna, JINR) ; Sada, C. (INFN, Padua) ; Salamida, F. (INFN, Milan Bicocca) ; Salathe, M. (Heidelberg, Max Planck Inst.) ; Schmitt, C. (Tubingen U.) ; Schneider, B. (Dresden, Tech. U.) ; Schönert, S. (Munich, Tech. U., Universe) ; Schreiner, J. (Heidelberg, Max Planck Inst.) ; Schulz, O. (Munich, Max Planck Inst.) ; Schütz, A.-K (Tubingen U.) ; Schwingenheuer, B. (Heidelberg, Max Planck Inst.) ; Selivanenko, O. (Moscow, INR) ; Shevchik, E. (Dubna, JINR) ; Shirchenko, M. (Dubna, JINR) ; Simgen, H. (Heidelberg, Max Planck Inst.) ; Smolnikov, A. (Heidelberg, Max Planck Inst.) ; Stanco, L. (INFN, Padua) ; Vanhoefer, L. (Munich, Max Planck Inst.) ; Vasenko, A.A. (Moscow, ITEP) ; Veresnikova, A. (Moscow, INR) ; Von Sturm, K. (INFN, Padua) ; Wagner, V. (Heidelberg, Max Planck Inst.) ; Walter, M. (Zurich U.) ; Wegmann, A. (Heidelberg, Max Planck Inst.) ; Wester, T. (Dresden, Tech. U.) ; Wiesinger, C. (Munich, Tech. U., Universe) ; Wojcik, M. (Jagiellonian U.) ; Yanovich, E. (Moscow, INR) ; Zhitnikov, I. (Dubna, JINR) ; Zhukov, S.V. (Kurchatov Inst., Moscow) ; Zinatulina, D. (Dubna, JINR) ; Zuber, K. (Dresden, Tech. U.) ; Zuzel, G. (Jagiellonian U.)

Pages: 14

Abstract: 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 ($0\nu\beta\beta$) decay should exist. The detection of this extremely rare hypothetical process requires utmost suppression of any kind of backgrounds. The GERDA collaboration searches for $0\nu\beta\beta$ 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 $0\nu\beta\beta$ 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 $0\nu\beta\beta$ decay motivates a larger germanium experiment with higher sensitivity.

Keyword(s): 0νββ decay ; $T^{0ν}_{1/2}$ ; $^{76}$Ge ; enriched Ge detectors ; active veto

Web-Page: http://inspirehep.net/record/1515730/files/exfig3-string2_3.png; http://inspirehep.net/record/1515730/files/exfig2-detector-geometry.png; http://inspirehep.net/record/1515730/files/exfig5-p-value-log.png; http://inspirehep.net/record/1515730/files/fig2-pII-2016.png; http://inspirehep.net/record/1515730/files/fig1-pII-2016.png; http://inspirehep.net/record/1515730/files/fig4-pII-2016.png; http://inspirehep.net/record/1515730/files/exfig1-g-7comp.png; http://inspirehep.net/record/1515730/files/exfig4a-fibers.png; http://inspirehep.net/record/1515730/files/exfig4c-bottom-shroud-crop.png; http://inspirehep.net/record/1515730/files/fig3-pII-2016.png; http://inspirehep.net/record/1515730/files/exfig4b-top-plate2-crop.png; http://inspirehep.net/record/1515730/files/arXiv:1703.00570.pdf


Note: 14 pages, 9 figures, 1 table

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