High-purity germanium detector ionization pulse shapes of nuclear recoils, gamma interactions and microphonism

TL;DR

This study analyzes pulse shapes in high-purity germanium detectors for nuclear recoils, gamma interactions, and microphonics, demonstrating the potential for pulse shape analysis to reduce background noise in dark matter detection.

Contribution

It provides the first measurements of microphonic noise pulse shapes and compares nuclear recoil and gamma pulse shapes, enhancing background discrimination techniques.

Findings

Pulse shapes of nuclear recoils and gamma interactions are similar.

Microphonic noise pulse shapes are characterized for the first time.

Pulse shape analysis can calibrate microphonic noise suppression methods.

Abstract

Nuclear recoil measurements with high-purity Germanium detectors are very promising to directly detect dark matter candidates. The main background sources in such experiments are natural radioactivity and microphonic noise. Digital pulse shape analysis is an encouraging approach to reduce the background originating from the latter. To study the pulse shapes of nuclear recoil events we performed a neutron scattering experiment, which covered the ionization energy range from 20 to 80 keV. We have measured ionization efficiencies as well and found an excellent agreement with the theory of Lindhard. In a further experiment we measured pulse shapes of a radioactive gamma-source and found no difference to nuclear recoil pulse shapes. Pulse shapes originating from microphonics of a HPGe-detector are presented for the first time. A microphonic noise suppression method, crucial for dark matter direct detection experiments, can therefore be calibrated with pulse shapes from gamma-sources.