Oxygen contamination in liquid Argon: combined effects on ionization electron charge and scintillation light

TL;DR

This study investigates how oxygen contamination affects ionization electron lifetime and scintillation light in liquid Argon, providing quantitative measurements of quenching effects over a range of oxygen concentrations.

Contribution

It presents the first combined measurement of oxygen's impact on both ionization and scintillation signals in liquid Argon, with a new quantification of the quenching rate constant.

Findings

Oxygen reduces scintillation long-lived component lifetime.

Electron lifetime correlates with oxygen concentration.

The quenching rate constant for oxygen in liquid Argon is 0.54±0.03 micros^-1 ppm^-1.

Abstract

A dedicated test of the effects of Oxygen contamination in liquid Argon has been performed at the INFN-Gran Sasso Laboratory (LNGS, Italy) within the WArP R&D program. Two detectors have been used: the WArP 2.3 lt prototype and a small (0.7 lt) dedicated detector, coupled with a system for the injection of controlled amounts of gaseous Oxygen. Purpose of the test with the 0.7 lt detector is to detect the reduction of the long-lived component lifetime of the Argon scintillation light emission at increasing O2 concentration. Data from the WArP prototype are used for determining the behavior of both the ionization electron lifetime and the scintillation long-lived component lifetime during the O2-purification process activated in closed loop during the acquisition run. The electron lifetime measurements allow to infer the O2 content of the Argon and correlate it with the long-lived scintillation lifetime data. The effect of Oxygen contamination on the scintillation light has been thus measured over a wide range of O2 concentration, spanning from about 10^-3 ppm up to about 10 ppm. The rate constant of the light quenching process induced by Oxygen in LAr has been found to be k'(O2)=0.54+-0.03 micros^-1 ppm^-1.