학술논문
Modeling backgrounds for the Majorana Demonstrator
Document Type
article
Author
Haufe, CR; Arnquist, IJ; Avignone, FT; Barabash, AS; Barton, CJ; Bhimani, KH; Blalock, E; Bos, B; Busch, M; Buuck, M; Caldwell, TS; Chan, Y-D; Christofferson, CD; Chu, P-H; Clark, ML; Cuesta, C; Detwiler, JA; Efremenko, Yu; Ejiri, H; Elliott, SR; Giovanetti, GK; Green, MP; Gruszko, J; Guinn, IS; Guiseppe, VE; Henning, R; Aguilar, D Hervas; Hoppe, EW; Hostiuc, A; Kidd, MF; Kim, I; Kouzes, RT; V., TE Lannen; Li, A; Lopez, AM; López-Castaño, JM; Martin, EL; Martin, RD; Massarczyk, R; Meijer, SJ; Oli, TK; Othman, G; Paudel, LS; Pettus, W; Poon, AWP; Radford, DC; Reine, AL; Rielage, K; Ruof, NW; Schaper, DC; Tedeschi, D; Varner, RL; Vasilyev, S; Wilkerson, JF; Wiseman, C; Xu, W; Yu, C-H; Zhu, BX
Source
AIP Conference Proceedings. 2908(1)
Subject
Language
Abstract
The MAJORANA DEMONSTRATOR is a neutrinoless double-beta decay (0νββ) experiment containing ~30 kg of p-type point-contact germanium detectors enriched to 88% in 76Ge and ~14 kg of natural germanium detectors. The detectors are housed in two electroformed copper cryostats and surrounded by a graded passive shield with an active muon veto. An extensive radioassay campaign was performed prior to installation to insure the use of ultra-clean materials. The DEMONSTRATOR achieved one of the lowest background rates in the region of the 0νββ Q-value, 15.7±1.4 cts/(FWHM t y) from the low-background configuration spanning most of the 64.5 kg-yr active exposure. Nevertheless this background rate is a factor of five higher than the projected background rate. This discrepancy arises from an excess of events from the 232Th decay chain. Background-model fits aim to explain the deviation from assay-based projections, potentially determine the source(s) of observed backgrounds, and allow a precise measurement of the two-neutrino double-beta decay half-life. The fits agree with earlier simulation studies, which indicate the origin of the 232Th excess is not from a near-detector component and have informed design decisions for the next-generation LEGEND experiment. Recent findings have narrowed the suspected locations for the excess activity, motivating a final simulation and assay campaign to complete the background model.