Analysis of the S1 triplet component in the DarkSide-50 experiment

TL;DR

This paper investigates how impurities, especially nitrogen, affect the triplet scintillation lifetime in the DarkSide-50 liquid argon detector, providing insights crucial for improving dark matter detection sensitivity.

Contribution

It presents a detailed analysis of impurity effects on triplet lifetime in LAr TPCs, focusing on nitrogen's role, and establishes a reference for purity levels in dark matter experiments.

Findings

Impurities reduce the triplet lifetime in LAr.

Nitrogen significantly quenches scintillation signals.

Triplet lifetime measurements can indicate argon purity levels.

Abstract

The DarkSide-50 (DS-50) experiment aims at the direct detection of weakly interacting massive particles. It is a dual-phase liquid argon time projection chamber (LAr TPC) where Dark Matter (DM), which constitutes five sixths of all matter in the universe, is expected to interact with an argon nucleus resulting in a nuclear recoil. A scintillation signal (S1) is produced as a result of the ionising events from the DM-Ar interaction. The impurities in LAr, such as $\text{O}_2, \text{N}_2, \text{H}_2\text{O}$, etc., at the ppm level, quench the scintillation photons, leading to a reduction in the observed lifetime of the triplet state. In this contribution, the effect of impurities on the triplet lifetime is analyzed for individual events using DS-50 data, with a primary focus on nitrogen, one of the candidates for the impurities in LAr hypothesized to cause a suppression of triplet lifetime. This is done by determining the lifetime of the triplet component with a known purity, which can be used as a reference for the purity level of argon used in current and future dark matter searches.