Internal Calibration of the PandaX-II Detector with Radon Gaseous Sources

TL;DR

This paper presents a novel low-energy electron recoil calibration method for the PandaX-II detector using radon gaseous sources, improving calibration accuracy for dark matter detection and informing future xenon detector calibrations.

Contribution

The study introduces a new calibration approach with $^{220}$Rn and $^{222}$Rn, demonstrating its effectiveness and applicability for large-scale xenon detectors like PandaX-4T.

Findings

Successful calibration with $^{220}$Rn over multiple campaigns

Measured background contribution from $^{214}$Pb for the first time in PandaX-II

Calibration strategy can be adopted in future xenon-based detectors

Abstract

We have developed a low-energy electron recoil (ER) calibration method with $^{220}$Rn for the PandaX-II detector. $^{220}$Rn, emanated from natural thorium compounds, was fed into the detector through the xenon purification system. From 2017 to 2019, we performed three dedicated calibration campaigns with different radon sources. We studied the detector response to $\alpha$, $\beta$, and $\gamma$ particles with focus on low energy ER events. During the runs in 2017 and 2018, the amount of radioactivity of $^{222}$Rn were on the order of 1\% of that of $^{220}$Rn and thorium particulate contamination was negligible, especially in 2018. We also measured the background contribution from $^{214}$Pb for the first time in PandaX-II with the help from a $^{222}$Rn injection. Calibration strategy with $^{220}$Rn and $^{222}$Rn will be implemented in the upcoming PandaX-4T experiment and can be useful for other xenon-based detectors as well.