Constraining Radon Backgrounds in LZ

TL;DR

This paper discusses the measurement and mitigation of radon backgrounds in the LZ dark matter detector, ensuring radon levels stay below the threshold necessary for successful rare-event detection.

Contribution

It presents a coordinated calibration and screening program across multiple institutions, along with preliminary results and mitigation strategies for radon backgrounds in LZ.

Findings

Radon levels estimated at <17.3 mBq, meeting science goals.

Calibration sources ensure consistent measurements across devices.

Mitigation strategies reduce radon production in key components.

Abstract

The LZ dark matter detector, like many other rare-event searches, will suffer from backgrounds due to the radioactive decay of radon daughters. In order to achieve its science goals, the concentration of radon within the xenon should not exceed $2\mu$Bq/kg, or 20 mBq total within its 10 tonnes. The LZ collaboration is in the midst of a program to screen all significant components in contact with the xenon. The four institutions involved in this effort have begun sharing two cross-calibration sources to ensure consistent measurement results across multiple distinct devices. We present here five preliminary screening results, some mitigation strategies that will reduce the amount of radon produced by the most problematic components, and a summary of the current estimate of radon emanation throughout the detector. This best estimate totals $<17.3$ mBq, sufficiently low to meet the detector's science goals.