Improved TPB-coated Light Guides for Liquid Argon TPC Light Detection Systems

TL;DR

This paper presents improved TPB-coated light guides with longer attenuation lengths for liquid argon TPCs, achieved through new coating, polishing, and dipping techniques, enabling better light detection in future large-scale detectors.

Contribution

It introduces a new acrylic-based coating and a hand-dipping method that significantly enhance light guide performance for liquid argon TPCs.

Findings

Attenuation lengths above 100 cm measured in air.

Model accurately predicts response in liquid argon.

Characterization in air suffices for quality control.

Abstract

Scintillation light produced in liquid argon (LAr) must be shifted from 128 nm to visible wavelengths in light detection systems used for liquid argon time-projection chambers (LArTPCs). To date, LArTPC light collection systems have employed tetraphenyl butadiene (TPB) coatings on photomultiplier tubes (PMTs) or plates placed in front of the PMTs. Recently, a new approach using TPB-coated light guides was proposed. In this paper, we report on light guides with improved attenuation lengths above 100 cm when measured in air. This is an important step in the development of meter-scale light guides for future LArTPCs. Improvements come from using a new acrylic-based coating, diamond-polished cast UV transmitting acrylic bars, and a hand-dipping technique to coat the bars. We discuss a model for connecting bar response in air to response in liquid argon and compare this to data taken in liquid argon. The good agreement between the prediction of the model and the measured response in liquid argon demonstrates that characterization in air is sufficient for quality control of bar production. This model can be used in simulations of light guides for future experiments.