Results of the MAJORANA DEMONSTRATOR’s Search for Double-Beta Decay of 76Ge to Excited States of 76Se

I S Guinn ,M F Kidd ,A L Reine ,M P Green ,Richard T Kouzes ,A Drobizhev,W Pettus,S J Meijer ,S R Elliott ,J M López-Castaño ,C D Christofferson ,R Massarczyk,Yu Efremenko,T Gilliss,R L Varner ,H Ejiri,F Bertrand ,W Xu,C Cuesta,F T Avignone ,T S Caldwell ,Pinghan Chu ,S Mertens,Michael Clark ,J F Wilkerson ,I J Arnquist ,In‐Wook Kim ,C Wiseman,G Othman,R Henning,J A Detwiler ,G K Giovanetti ,K Rielage,J Rager,T K Oli ,A S Barabash ,A W P Poon ,N W Ruof ,M Busch,C R Haufe ,E L Martín ,D C Radford ,C.‐H Yu ,A Hostiuc,B Bos,D W Edwins,R D Martin ,R J Hegedus ,A López ,M J Stortini ,Y-D Chan,D J Tedeschi ,C J Barton,D Hervas Aguilar,J Gruszko,J Myslik,E W Hoppe ,V E Guiseppe ,M Buuck,B X Zhu

doi:10.1088/1742-6596/1468/1/012115

Abstract

The MAJORANA DEMONSTRATOR is searching for double-beta decay of 76Ge to excited states (E.S.) in 76Se using a modular array of high purity Germanium detectors. 76Ge can decay into three E.S.s of 76Se. The E.S. decays have a clear event signature consisting of a ββ-decay with the prompt emission of one or two γ-rays, resulting in with high probability in a multi-site event. The granularity of the DEMONSTRATOR detector array enables powerful discrimination of this event signature from backgrounds. Using 21.3 kg-y of isotopic exposure, the DEMONSTRATOR has set world leading limits for each E.S. decay, with 90% CL lower half-life limits in the range of (0.56 ‒ 2.1) ⋅ 1024 y. In particular, for the 2v transition to the first 0+ E.S. of 76Se, a lower half-life limit of 0.68 ⋅ 1024 at 90% CL was achieved.

Highlights

Double-beta (ββ) decay is the subject of a varied experimental program. Of particular interest is neutrinoless double-beta decay (0νββ), a hypothetical lepton number violating process that would indicate that the neutrino is a Majorana fermion
Double-beta decay is the subject of a varied experimental program
Since 95% of 76Ge is contained in enriched detectors and the ββ site will be contained in a separate detector from the gamma peak, events in which none of the coincident detectors are enriched are cut

Summary

Introduction

Double-beta (ββ) decay is the subject of a varied experimental program. Of particular interest is neutrinoless double-beta decay (0νββ), a hypothetical lepton number violating process that would indicate that the neutrino is a Majorana fermion. Because ββ to E.S. is an inherently multi-site event, the Demonstrator can significantly reduce its backgrounds by searching only for events that involve multiple detector hits.

Results

Conclusion