Application and modeling of an online distillation method to reduce krypton and argon in XENON1T

TL;DR

This paper presents a novel online cryogenic distillation method for XENON1T that significantly reduces krypton and argon backgrounds, achieving record low krypton levels and enabling new calibration techniques.

Contribution

It introduces an innovative online distillation technique and a comprehensive model for krypton and argon removal in dark matter detectors, improving background reduction and calibration methods.

Findings

Achieved krypton concentration of (360 ± 60) ppq in XENON1T.

Successfully removed Ar-37 after calibration injections.

Developed a model to optimize future large-scale detector distillation strategies.

Abstract

A novel online distillation technique was developed for the XENON1T dark matter experiment to reduce intrinsic background components more volatile than xenon, such as krypton or argon, while the detector was operating. The method is based on a continuous purification of the gaseous volume of the detector system using the XENON1T cryogenic distillation column. A krypton-in-xenon concentration of $(360 \pm 60)$ ppq was achieved. It is the lowest concentration measured in the fiducial volume of an operating dark matter detector to date. A model was developed and fit to the data to describe the krypton evolution in the liquid and gas volumes of the detector system for several operation modes over the time span of 550 days, including the commissioning and science runs of XENON1T. The online distillation was also successfully applied to remove Ar-37 after its injection for a low energy calibration in XENON1T. This makes the usage of Ar-37 as a regular calibration source possible in the future. The online distillation can be applied to next-generation experiments to remove krypton prior to, or during, any science run. The model developed here allows further optimization of the distillation strategy for future large scale detectors.