Progress Toward A 2νββ Measurement For The Majorana Demonstrator

T Gilliss ,V Yumatov ,E W Hoppe ,B R White ,A W P Poon ,A L Reine ,C Dunagan ,J E Trimble ,T Bode ,F T Avignone ,M Busch ,С И Коновалов ,I S Guinn ,G Othman ,I Zhitnikov ,R L Varner ,S I Alvis ,A Bradley ,T S Caldwell ,N W Ruof ,C.‐H Yu ,N Abgrall ,K Rielage ,Y V Efremenko ,A López ,M Shirchenko ,A S Barabash ,J Myslik ,H Ejiri ,C J Barton ,C Wiseman ,M A Howe ,Y D Chan ,A M Suriano ,E Yakushev ,I J Arnquist ,M F Kidd ,B Shanks ,K Vorren ,J Gruszko ,Richard T Kouzes ,S J Meijer ,F Bertrand ,D J Tedeschi ,S Mertens ,R Henning ,C D Christofferson ,S Vasilyev ,K Vetter ,M Buuck ,C Cuesta ,W Xu ,C O’shaughnessy ,Pinghan Chu ,K J Keeter ,C R Haufe ,J A Detwiler ,W Pettus ,R Massarczyk ,D C Radford ,L Hehn ,S R Elliott ,V Brudanin ,V E Guiseppe ,R D Martin ,J F Wilkerson ,M P Green ,J Rager ,G K Giovanetti ,R G H Robertson ,B X Zhu

doi:10.1088/1742-6596/1342/1/012117

Abstract

The MAJORANA DEMONSTRATOR is a 76Ge-based neutrinoless double-beta decay (0νββ) experiment. Staged at the 4850 ft level of the Sanford Underground Research Facility, the DEMONSTRATOR operates an array of high-purity p-type point contact Ge detectors deployed within a graded passive shield and an active muon veto system. The present work concerns the two-neutrino double-beta decay mode (2νββ) of 76Ge. For Ge detectors, having superior energy resolution (0.1%), this mode poses negligible background to the 0νββ mode, even for a ton-scale experiment. However, the measurement of the 2νββ mode allows for careful systematics checks of active detector mass, enrichment fraction, and pulse shape discrimination cuts related to both the 0νββ and 2νββ decay modes. A precision measurement of the 2νββ shape also allows searches for spectral distortions, possibly indicative of new physics, including 0νββχ. Work is underway to construct a full experimental background model enabling a Bayesian fit to the measured energy spectrum and extraction of a precise 2νββ spectrum and half-life.

Highlights

The Majorana Demonstrator has deployed two arrays of high-purity Ge (HPGe) crystals, 29.7 kg of which are enriched to 88% in 76Ge
Outlook To date, the Majorana Demonstrator has accumulated an appreciable exposure of HPGe detectors under low-background conditions, and a simulation campaign informed by materials assay has studied the transport of radiation through a detailed model of the experimental setup
Work is ongoing to constrain the location and importance of various background contributions, with insights guiding a full fit to the experimental energy spectrum

Summary

Introduction

The Majorana Demonstrator has deployed two arrays of high-purity Ge (HPGe) crystals, 29.7 kg of which are enriched to 88% in 76Ge. Assay techniques measure or set upper limits on the specific activity of each material, and those results are scaled based on efficiencies determined in Monte Carlo simulations that account for the detailed experimental geometry.

Results

Conclusion