Direct comparison of PEN and TPB wavelength shifters in a liquid argon detector

Abstract

A large number of particle detectors employ liquid argon as their target material owing to its high scintillation yield and its ability to drift ionization charge over large distances. Scintillation light from argon is peaked at 128 nm and a wavelength shifter is required for its efficient detection. In this work, we directly compare the light yield achieved in two identical liquid argon chambers, one of which is equipped with polyethylene naphthalate (PEN) and the other with tetraphenyl butadiene (TPB) wavelength shifter. Both chambers are lined with enhanced specular reflectors and instrumented with SiPMs with a coverage fraction of approximately 1%, which represents a geometry comparable to the future large scale detectors. We measured the light yield of the PEN chamber to be 39.4$$\,\pm \,$$ ± 0.4(stat)$$\,\pm \,$$ ± 1.9(syst)% of the yield of the TPB chamber. Using a Monte Carlo simulation this result is used to extract the wavelength shifting efficiency of PEN relative to TPB equal to 47.2$$\,\pm \,$$ ± 5.7%. This result paves the way for the use of easily available PEN foils as a wavelength shifter, which can substantially simplify the construction of future liquid argon detectors.

SiPM cross-talk in liquid argon detectors

“…The mean number of photo-electrons observed by both photo-detectors is extracted by fitting the calibration peak with a Gaussian model [9]. The gross light yield, referred to as LY OV G hereafter, is given by the ratio between the number of detected photo-electrons and the energy deposited in the medium by the source in use.…”

“…There are several issues on the modeling of the optics, among which the most important ones are: (1) the nature of the optical interface between the fused-silica window and TPB is not well understood and (2) the reflectivity of the SiPM, which has a multi-layer antireflective coating, has been measured in air and pro-jected to LAr medium [9]. These affect the aforementioned light collection efficiency and hence we estimate a systematic error of ±5 % on the absolute value.…”

“…The detectors were installed in a sealed dewar inside a container filled with about 4 L of high purity argon, within the STAR facility [9]. The system provides argon constantly purified by a getter (SAES PS4-MT3) in a re-circulation loop with a flow of 5 sl/min.…”

“…The after-pulse (AP) was studied in [9] and for the over-voltage in use it doesn't exceed 10 %. Therefore, to a first approximation, it can be neglected.…”

Very large SiPM arrays with aggregated output

“…1: Electrical parameters of the SiPMs and of the assembled tiles in liquid nitrogen. The first section documents the electrical parameters of the single SiPMs: the NUV-HD-LF column refers to the devices studied in [5][6][7], while the NUV-HD-Cryo are the subject of this work and have been documented in [8][9][10]. For the breakdown voltage and for the quenching resistance the error term describes the standard deviation of the population, rather than a measurement uncertainty.…”