Abstract
For the first time, planar high-purity germanium detectors with thin amorphous germanium contacts were successfully operated directly in liquid nitrogen and liquid argon in a cryostat at the Max-Planck-Institut für Physics in Munich. The detectors were fabricated at the Lawrence Berkeley National Laboratory and the University of South Dakota, using crystals grown at the University of South Dakota. They survived long-distance transportation and multiple thermal cycles in both cryogenic liquids and showed reasonable leakage currents and spectroscopic performance. Also discussed are the pros and cons of using thin amorphous semiconductor materials as an alternative contact technology in large-scale germanium experiments searching for physics beyond the Standard Model.
Highlights
If the decay of heavy Majorana neutrinos [1,2,3,4] in the early universe into leptons and antileptons created a slight matter and antimatter asymmetry [5,6], the observed asymmetry in our current universe can be explained with the help of Leptogenesis [7,8], which is a theory that converts the lepton– antilepton asymmetry to a baryon–antibaryon asymmetry
A dozen mini planar detectors have been fabricated at the University of South Dakota (USD) using the technique developed at Lawrence Berkeley National Laboratory (LBNL) and high-purity germanium (HPGe) crystals produced at the USD crystal pulling facility [38]
2.98 a Net impurity concentration calculated using Eq 1. b Made by Mark Amman at LBNL in 2015. c Values are for the central contact. d Vd : Depletion voltage. e I : leakage current measured at 1200 V in LN2, liquid argon (LAr), and vacuum before/after the MPI deployment f ΔE: energy resolutions of the pulser and the 662 keV γ -ray peak measured at 1200 V in LN2, LAr and vacuum before/after the MPI
Summary
If the decay of heavy Majorana neutrinos [1,2,3,4] in the early universe into leptons and antileptons created a slight matter and antimatter asymmetry [5,6], the observed asymmetry in our current universe can be explained with the help of Leptogenesis [7,8], which is a theory that converts the lepton– antilepton asymmetry to a baryon–antibaryon asymmetry. An additional consideration are background events mimicking 0νββ decays, induced by electrons from beta decays on the surface of the detector. Signals from a surface segment normally have worse energy resolution than those from the point-contact due to the larger capacitance of the segment. They can be used to precisely determine the start time of an event in a PPC, especially of an event close to the surface. A dozen mini planar detectors have been fabricated at the University of South Dakota (USD) using the technique developed at LBNL and HPGe crystals produced at the USD crystal pulling facility [38] They perform well in a traditional vacuum cryostat [39]. Reported in this paper is work carried out in summer 2019 to study the feasibility of operating HPGe detectors with thin amorphous germanium surfaces directly in LN2 and LAr
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