LArRI — A new setup for Liquid Argon Refractive index measurement

Liquid argon (LAr), widely used as the active target in neutrino and dark matter experiments, is a scintillator with a light yield of approximately 40 photons/keV. The scintillation spectrum is centered at 128 nm, and the attenuation length is of the order of meters, depending on the purity. The addition of small amounts of dopants allows for shifting the scintillation peak simplifying the light detection and opening the possibility to the development of imaging systems. There is no precise knowledge of the optical properties of LAr in the VUV range, but it could be exploited to improve the performances of liquid argon-based experiments, especially when the involved mass is in the ton scale. LArRI (Liquid Argon Refractive Index) aims to directly measure the refractive index of LAr in the VUV spectrum, using an interferometric technique. The refractive index is obtained by comparing two interference patterns, created in vacuum and liquid, acquired with cryogenic silicon photomultipliers. This work primarily presents the methodology, the preliminary tests, and the analysis strategy, which are intended to be applied to real data shortly.