Demonstration of the light collection stability of a PEN-based wavelength shifting reflector in a tonne scale liquid argon detector

TL;DR

This study evaluates the stability of PEN as a wavelength shifter in a large-scale liquid argon detector, demonstrating no performance deterioration over 12 days, suggesting PEN's viability as an alternative to TPB.

Contribution

The paper provides the first large-scale stability assessment of PEN in a tonne-scale liquid argon detector, supporting its potential as a practical wavelength shifter substitute.

Findings

No performance deterioration of PEN over 12 days

PEN shows stable light collection in large-scale setup

Supports PEN as a feasible alternative to TPB

Abstract

Liquid argon detectors rely on wavelength shifters for efficient detection of scintillation light. The current standard is tetraphenyl butadiene (TPB), but it is challenging to instrument on a large scale. Poly(ethylene 2,6-naphthalate) (PEN), a polyester easily manufactured as thin sheets, could simplify the coverage of large surfaces with wavelength shifters. Previous measurements have shown that commercial grades of PEN have approximately 50% light conversion efficiency relative to TPB. Encouraged by these results, we conducted a large-scale measurement using $4~m^2$ combined PEN and specular reflector foils in a two-tonne liquid argon dewar to assess its stability over approximately two weeks. This test is crucial for validating PEN as a viable substitute for TPB. The setup used for the measurement of the stability of PEN as a wavelength shifter is described, together with the first results, showing no evidence of performance deterioration over a period of 12 days.