On an unverified nuclear decay and its role in the DAMA experiment

TL;DR

This paper investigates an unmeasured nuclear decay of potassium-40, its impact as a background in the DAMA dark matter experiment, and how it challenges the dark matter interpretation of DAMA's results.

Contribution

It reports the first analysis of a unique potassium-40 decay and assesses its significance as a background in dark matter detection experiments.

Findings

Unmeasured decay rate of 40K to 40Ar ground state analyzed.

Potassium contamination levels affect dark matter signal interpretation.

Higher potassium contamination challenges the dark matter explanation for DAMA results.

Abstract

The rate of the direct decay of 40K to the ground state of 40Ar through electron capture has not been experimentally reported. Aside from its inherent importance for the theory of electron capture as the only such decay known of its type (unique third-forbidden), this decay presents an irreducible background in the DAMA experiment. We find that the presence of this background, as well as others, poses a challenge to any interpretation of the DAMA results in terms of a Dark Matter model with a small modulation fraction. A 10ppb contamination of natural potassium requires a 20% modulation fraction or more. A 20ppb contamination, which is reported as an upper limit by DAMA, disfavors any Dark Matter origin of the signal. This conclusion is based on the efficiency of detecting 40K decays as inferred from simulation. We propose measures to help clarify the situation.