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Search for neutrinoless double- β decay in Ge 76 with 26 kg yr of exposure from the M ajorana D emonstrator SEARCH for NEUTRINOLESS DOUBLE- β DECAY ... S. I. ALVIS et al.

  • Author(s): Cuesta, C;
  • Alvis, SI;
  • Arnquist, IJ;
  • Avignone, FT;
  • Barabash, AS;
  • Barton, CJ;
  • Basu, V;
  • Bertrand, FE;
  • Bos, B;
  • Busch, M;
  • Buuck, M;
  • Caldwell, TS;
  • Chan, YD;
  • Christofferson, CD;
  • Chu, PH;
  • Clark, M;
  • Cuesta, C;
  • Detwiler, JA;
  • Efremenko, Y;
  • Ejiri, H;
  • Elliott, SR;
  • Gilliss, T;
  • Giovanetti, GK;
  • Green, MP;
  • Gruszko, J;
  • Guinn, IS;
  • Guiseppe, VE;
  • Haufe, CR;
  • Hegedus, RJ;
  • Hehn, L;
  • Henning, R;
  • Hervas Aguilar, D;
  • Hoppe, EW;
  • Howe, MA;
  • Kidd, MF;
  • Konovalov, SI;
  • Kouzes, RT;
  • Lopez, AM;
  • Martin, RD;
  • Massarczyk, R;
  • Meijer, SJ;
  • Mertens, S;
  • Myslik, J;
  • Othman, G;
  • Pettus, W;
  • Piliounis, A;
  • Poon, AWP;
  • Radford, DC;
  • Rager, J;
  • Reine, AL;
  • Rielage, K;
  • Ruof, NW;
  • Shanks, B;
  • Shirchenko, M;
  • Tedeschi, D;
  • Varner, RL;
  • Vasilyev, S;
  • White, BR;
  • Wilkerson, JF;
  • Wiseman, C;
  • Xu, W;
  • Yakushev, E;
  • Yu, CH;
  • Yumatov, V;
  • Zhitnikov, I;
  • Zhu, BX
  • et al.

The Majorana Collaboration is operating an array of high-purity Ge detectors to search for the neutrinoless double-β decay of Ge76. The Majorana Demonstrator consists of 44.1 kg of Ge detectors (29.7 kg enriched to 88% in Ge76) split between two modules constructed from ultraclean materials. Both modules are contained in a low-background shield at the Sanford Underground Research Facility in Lead, South Dakota. We present updated results on the search for neutrinoless double-β decay in Ge76 with 26.0±0.5 kg yr of enriched exposure. With the Demonstrator's energy resolution of 2.53 keV FWHM at Qββ, which is the best among all neutrinoless double-β decay experiments, we observe one event in the region of interest with 0.65 events expected from the estimated background, resulting in a lower limit on the Ge76 neutrinoless double-β decay half-life of 2.7×1025 yr [90% confidence level (CL)] with a median sensitivity of 4.8×1025 yr (90% CL). Depending on the matrix elements used, a 90% CL upper limit on the effective Majorana neutrino mass in the range of 200-433 meV is obtained. The measured background in the configurations with full shielding and optimized grounding is 11.9±2.0 counts/(FWHM t yr).

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