3D Modeling of Electric Fields in the LUX Detector

TL;DR

This paper presents a detailed 3D electric field model for the LUX detector, accounting for time-varying charge effects that influence event reconstruction during WIMP searches.

Contribution

It introduces a method to model and map the evolving 3D electric fields in the LUX detector using COMSOL and calibration data, improving event analysis accuracy.

Findings

Electric field varied over time but maintained an average magnitude of ~200 V/cm.

Modeled charge density on PTFE panels increased from -3.6 to -5.5 μC/m².

The model successfully accounted for electric field variations affecting event reconstruction.

Abstract

This work details the development of a three-dimensional (3D) electric field model for the LUX detector. The detector took data during two periods of searching for weakly interacting massive particle (WIMP) searches. After the first period completed, a time-varying non-uniform negative charge developed in the polytetrafluoroethylene (PTFE) panels that define the radial boundary of the detector's active volume. This caused electric field variations in the detector in time, depth and azimuth, generating an electrostatic radially-inward force on electrons on their way upward to the liquid surface. To map this behavior, 3D electric field maps of the detector's active volume were built on a monthly basis. This was done by fitting a model built in COMSOL Multiphysics to the uniformly distributed calibration data that were collected on a regular basis. The modeled average PTFE charge density increased over the course of the exposure from -3.6 to $-5.5~\mu$C/m$^2$. From our studies, we deduce that the electric field magnitude varied while the mean value of the field of $\sim200$~V/cm remained constant throughout the exposure. As a result of this work the varying electric fields and their impact on event reconstruction and discrimination were successfully modeled.