Charge Trapping and Energy Performance of the MAJORANA DEMONSTRATOR

TL;DR

This paper investigates charge trapping in PPC germanium detectors used in the MAJORANA DEMONSTRATOR, proposing correction methods that significantly improve energy resolution crucial for neutrinoless double-beta decay detection.

Contribution

It introduces a modified digital pole-zero correction and an alternative method to counter charge trapping effects, enhancing energy resolution in PPC detectors.

Findings

Charge trapping degrades energy resolution by ~30%.

Proposed corrections improve resolution to ~2.4 keV FWHM at 2039 keV.

Methods are effective for enhancing detector performance in rare event searches.

Abstract

P-type point contact (PPC) high-purity germanium detectors are an important technology in astroparticle and nuclear physics due to their superb energy resolution, low noise, and pulse shape discrimination capabilities. Analysis of data from the MAJORANA DEMONSTRATOR, a neutrinoless double-beta decay experiment deploying PPC detectors enriched in $^{76}$Ge, has led to several novel improvements in the analysis of PPC signals. In this work we discuss charge trapping in PPC detectors and its effect on energy resolution. Small dislocations or impurities in the crystal lattice result in trapping of charge carriers from an ionization event of interest, attenuating the signal and degrading the measured energy. We present a modified digital pole-zero correction to the signal energy estimation that counters the effects of charge trapping and improves the energy resolution of the MAJORANA DEMONSTRATOR by approximately 30% to around 2.4 keV FWHM at 2039 keV, the $^{76}$Ge $Q$-value. An alternative approach achieving similar resolution enhancement is also presented.