Measurement of Space Charge Effects in the MicroBooNE LArTPC Using Cosmic Muons

TL;DR

This paper presents methods to measure and correct space charge effects in large liquid argon TPCs like MicroBooNE using cosmic muons, improving spatial accuracy by addressing ion-induced distortions.

Contribution

It introduces novel calibration techniques employing cosmic muons and track pairs to quantify and correct three-dimensional spatial distortions in LArTPCs.

Findings

Calibration techniques effectively measure space charge distortions.

Monte Carlo and MicroBooNE data validate the correction methods.

UV laser system estimates systematic biases.

Abstract

Large liquid argon time projection chambers (LArTPCs), especially those operating near the surface, are susceptible to space charge effects. In the context of LArTPCs, the space charge effect is the build-up of slow-moving positive ions in the detector primarily due to ionization from cosmic rays, leading to a distortion of the electric field within the detector. This effect leads to a displacement in the reconstructed position of signal ionization electrons in LArTPC detectors ("spatial distortions"), as well as to variations in the amount of electron-ion recombination experienced by ionization throughout the volume of the TPC. We present techniques that can be used to measure and correct for space charge effects in large LArTPCs by making use of cosmic muons, including the use of track pairs to unambiguously pin down spatial distortions in three dimensions. The performance of these calibration techniques are studied using both Monte Carlo simulation and MicroBooNE data, utilizing a UV laser system as a means to estimate the systematic bias associated with the calibration methodology.