Depth Requirements for a Tonne-scale 76Ge Neutrinoless Double-beta Decay Experiment
The MAJORANA Collaboration, E. Aguayo, F. T. Avignone, H. O. Back, A. S. Barabash, M. Bergevin, F. E. Bertrand, M. Boswell, V. Brudanin, M. Busch, Y-D. Chan, C.… 展开作者
The MAJORANA Collaboration, E. Aguayo, F. T. Avignone, H. O. Back, A. S. Barabash, M. Bergevin, F. E. Bertrand, M. Boswell, V. Brudanin, M. Busch, Y-D. Chan, C. D. Christofferson, J. I. Collar, D. C. Combs, R. J. Cooper, J. A. Detwiler, P. J. Doe, Yu. Efremenko, V. Egorov, H. Ejiri, S. R. Elliott, J. Esterline, J. E. Fast, N. Fields, P. Finnerty, F. M. Fraenkle, V. M. Gehman, G. K. Giovanetti, M. P. Green, V. E. Guiseppe, K. Gusey, A. L. Hallin, R. Hazama, R. Henning, A. Hime, E. W. Hoppe, M. Horton, S. Howard, M. A. Howe, R. A. Johnson, K. J. Keeter, M. E. Keillor, C. Keller, J. D. Kephart, M. F. Kidd, A. Knecht, O. Kochetov, S. I. Konovalov, R. T. Kouzes, B. D. LaFerriere, B. H. LaRoque, J. Leon, L. E. Leviner, J. C. Loach, S. MacMullin, M. G. Marino, R. D. Martin, D. -M. Mei, J. H. Merriman, M. L. Miller, L. Mizouni, M. Nomachi, J. L. Orrell, N. R. Overman, D. G. Phillips, A. W. P. Poon, G. Perumpilly, G. Prior, D. C. Radford, K. Rielage, R. G. H. Robertson, M. C. Ronquest, A. G. Schubert, T. Shima, M. Shirchenko, K. J. Snavely, V. Sobolev, D. Steele, J. Strain, K. Thomas, V. Timkin, W. Tornow, I. Vanyushin, R. L. Varner, K. Vetter, K. Vorren, J. F. Wilkerson, B. A. Wolfe, E. Yakushev, A. R. Young, C. -H. Yu, V. Yumatov, C. Zhang
备注：
Corresponding author: J. Detwiler (jasondet@uw.edu), 25 pages, 2 figures
Neutrinoless double-beta decay experiments can potentially determine the Majorana or Dirac nature of the neutrino, and aid in understanding the neutrino absolute mass scale and hierarchy. Future 76Ge-based searches target a half-life sensitivity of >10^27 y to explore the inverted neutrino mass hierarchy. Reaching this sensitivity will require a background rate of <1 count tonne^-1 y^-1 in a 4-keV-wide spectral region of interest surrounding the Q value of the decay. We investigate the overburden required to reach this background goal in a tonne-scale experiment with a compact (copper and lead) shield based on Monte Carlo calculations of cosmic-ray background rates. We find that, in light of the presently large uncertainties in these types of calculations, a site with an underground depth >~5200 mwe is required for a tonne-scale experiment with a compact shield similar to the planned 40-kg MAJORANA DEMONSTRATOR. The required overburden is highly dependent on the chosen shielding configuration and could be relaxed significantly if, for example, a liquid cryogen and water shield, or an active neutron shield were employed. Operation of the MAJORANA DEMONSTRATOR and GERDA detectors will serve to reduce the uncertainties on cosmic-ray background rates and will impact the choice of shielding style and location for a future tonne-scale experiment.
4/2013: The peer review process revealed that one of the veto rejection factors (the factor-of-4 described on p12) needs to be better established. Our reevaluation of this parameter to date has not yielded strong support for the value stated in the manuscript, and we require further study to develop a solid estimate. This further study will supersede the work described in this manuscript, and may or may not lead to the same conclusion regarding the ~>5200 mwe requirement for future tonne-scale 76Ge neutrinoless double beta decay experiments.
The MAJORANA DEMONSTRATOR: Progress towards showing the feasibility of a tonne-scale 76Ge neutrinoless double-beta decay experiment
马约拉纳演示器将使用浓缩和天然锗探测器的混合阵列来搜索76 Ge同位素的无中微子双β衰变。对这种罕见衰变的观测表明中微子是它自己的反粒子，证明轻子数不守恒，并提供中微子绝对质量尺度的信息。演示器正在南达科他州Lead的Sanford地下研究设施的4850英尺高度组装。该阵列将被包含在低背景环境中，并被被动和主动屏蔽所包围。演示器的目标是：在2039 keV 76 Ge端点能量周围的4 keV感兴趣区域（ROI）中演示小于3 t $^{-1}$ y $^{-1}$的本底率;建立建造吨级锗基双β衰变实验所需的技术;测试最近观测到无中微子双β衰变的声明[H. V. Klapdor-Kleingrothaus和I. V. Krivosheina，Mod. Phys. Lett. A21，1547（2006）];以及直接搜索轻WIMP（3-10 GeV）。
Addendum to: QRPA uncertainties and their correlations in the analysis of neutrinoless double beta decay
在以前的文章[Phys. Rev. D 79，053001（2009）]中，我们在准粒子无规相位近似（QRPA）中估计了与无中微子双β衰变（0 nu β β）的核矩阵元（NME）相关的不确定性。这种估计包括最近对NME的独立计算，因此仍然可以提供核模型不确定性的公平代表。在这种情况下，我们比较了Ge-76中0 nu β β衰变的声明与最近在Ge-136和其他核中的负结果，并推断了在90% C. L.时允许或排除的寿命范围。我们还强调了一些问题，应加以解决，以适当地比较和结合来自不同的0 nu β β衰变候选核的结果。
