Results from the first use of low radioactivity argon in a dark matter search

TL;DR

This paper reports the first dark matter search results using low-radioactivity argon in a liquid argon detector, achieving a background-free null result and setting new upper limits on WIMP interactions.

Contribution

It demonstrates the use of underground argon with significantly reduced Ar-39 levels in a large-scale liquid argon detector for dark matter searches, providing new constraints on WIMP-nucleon cross sections.

Findings

Achieved a background-free null result over 70.9 live-days.

Reduced Ar-39 levels by a factor of approximately 1400.

Set new upper limits on WIMP-nucleon cross sections at various masses.

Abstract

Liquid argon is a bright scintillator with potent particle identification properties, making it an attractive target for direct-detection dark matter searches. The DarkSide-50 dark matter search here reports the first WIMP search results obtained using a target of low-radioactivity argon. DarkSide-50 is a dark matter detector, using two-phase liquid argon time projection chamber, located at the Laboratori Nazionali del Gran Sasso. The underground argon is shown to contain Ar-39 at a level reduced by a factor (1.4 +- 0.2) x 10^3 relative to atmospheric argon. We report a background-free null result from (2616 +- 43) kg d of data, accumulated over 70.9 live-days. When combined with our previous search using an atmospheric argon, the 90 % C.L. upper limit on the WIMP-nucleon spin-independent cross section based on zero events found in the WIMP search regions, is 2.0 x 10^-44 cm^2 (8.6 x 10^-44 cm^2, 8.0 x 10^-43 cm^2) for a WIMP mass of 100 GeV/c^2 (1 TeV/c^2 , 10 TeV/c^2).