Comments on "A Dark Matter Search with MALBEK"

TL;DR

This paper critiques MALBEK's low-mass dark matter search, revealing that its data acquisition electronics and the W_par parameter limit its ability to distinguish surface from bulk events at low energies, overstating its sensitivity.

Contribution

It clarifies the physical meaning of W_par and demonstrates its inability to effectively discriminate events below 1 keVee, challenging previous sensitivity claims.

Findings

W_par does not correlate with rise-time at low energy

MALBEK's electronics limit surface-bulk event discrimination

Sensitivity to low-mass dark matter is overstated due to this limitation

Abstract

CoGeNT and MALBEK use p-type point contact germanium detectors to search for low-mass dark matter particles. Both detectors enjoy identical intrinsic noise characteristics. However, MALBEK's data acquisition electronics severely degrade the ability to separate signals originating in the bulk of the germanium crystal from surface backgrounds, through a measurement of the preamplifier pulse rise-time in the sub-keVee energy range of interest. The physical meaning of the parameter W$_{par}$ developed by the MAJORANA collaboration to compensate for this limitation is clarified here. It is shown that this parameter does not correlate to rise-time at low energy, and is presently unable to distinguish between surface and bulk events below $\sim$1 keVee. This leads to a sizable overstatement of MALBEK's sensitivity to low-mass dark matter particles, when employing aggressive W$_{par}$ cuts.