Scintillation photons in liquid argon (LAr) exhibit peculiar behavior due to their short wavelength (128 nm). Anne Chappuis, a PhD student at the Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP) in France, wants to understand this behavior. She collaborates with colleagues from the LAPP, APC, CIEMAT and IFAE institutes on ProtoDUNE-DP.
Last year, after improving the method for producing 3D light maps of the detector that parametrize the photon propagation, Chappuis produced maps for the dual-phase detectors. She also performed a detailed study of the behavior of the scintillation photons in LAr, which revealed major impacts on the light collection from Rayleigh scattering and from absorption by stainless steel and by the LAr itself. These scintillation light studies provided input to the ProtoDUNE-DP design, in particular, concerning the positioning of the photomultipliers.
“This is an important subject in the context of the ProtoDUNE and DUNE experiments,” said Anne’s supervisor, Isabelle Debonis, associate professor at Savoie Mont-Blanc University, adding that Anne is making great progress in understanding light detection in the liquid argon TPC.
“In ProtoDUNE-DP, we expect a very high flux of cosmic muons that will lead to the production of a huge number of photons,” Chappuis said. “Simulating the precise trajectory of each of them is inefficient, so instead we perform this simulation only once, store the useful information — the probability of detection and detection time — in the light maps, and use these values when we simulate the light signal.”
Chappuis is developing an algorithm to tag and reject the cosmic muon background expected in ProtoDUNE-DP.
“I am trying to understand the impact of the detector design on the light collection,” she said. “The comparison between the 3x1x1 detector simulation and the light data will allow me to improve the current simulation and constrain the parameter values that will be used in the final simulations for ProtoDUNE-DP.”
Also contributing to the light signal analysis and simulation for the dual-phase detectors is Clara Cuesta, a postdoc from the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT) in Spain. Having joined DUNE in February 2017, Cuesta is already making her mark.
“Clara’s commitment, seriousness and rigor at work are outstanding,” said her supervisor, CIEMAT senior researcher Inés Gil Botella. Cuesta has been appointed convener of the light-calibration working group in the Dual Phase Photon Detection Consortium.
The ProtoDUNE-DP light-detection system consists of 36 cryogenic photomultipliers. Cuesta and her colleagues at CIEMAT are characterizing these photomultipliers (PMTs) to determine their gain and stability in response to different light signals.
“To verify the correct functioning of the photomultipliers, we designed and tested a light-calibration system for the ProtoDUNE-DP detector,” said Cuesta. She and her team used a system of LEDs with optical fibers to provide a homogeneous and configurable amount of light to each PMT. The team performed several tests to quantify the light losses of this design, with successful results.
“However, the extension to DUNE is challenging. Simply scaling the system would imply the addition of many light fibers and LEDs, and it is likely that a redesign will take place,” she said. She addied that the ProtoDUNE-DP results will be key to quantifying the absolute amount of light per PMT required to measure the gain, monitor the stability, and to study the performance of the fibers in cryogenic conditions.
“Clara’s work has been critical to providing the most performant and cost-effective light calibration system for protoDUNE-DP,” said Botella.