Scintillation imaging in GRAIN Liquid Argon detector of DUNE experiment

Abstract GRAIN (GRanular Argon for Interaction of Neutrinos) is a Liquid Argon detector which is part of the Near Detector complex of DUNE experiment. Most conventional noble liquid detectors employ scintillation light as either a timing signal for a TPC or as a calorimetric measurement, or both. The signal's relative amplitude and timing on multiple detectors can also be used to approximately locate an interaction. In GRAIN we go a step further, by using scintillation light to reconstruct images of tracks associated to charge particles in Liquid Argon volume. In fact, by developing a suitable optical system, coupled with finely segmented SiPM arrays, it is possible to build photographic cameras that capture images of the primary scintillation light. In absence of a TPC, scintillation imaging alone can provide vertexing and tracking information, while combined it can enhance resolution and rate capability (which is a concern for near detectors located on powerful neutrino beams). Argon scintillates in the VUV range, imposing stringent requirements on the optical system and SiPMs. By replacing a traditional set of lenses with lenses built with materials specifically designed to operate in cryogenic conditions or with coded aperture masks, a compact camera can be created. The latest results from simulation and reconstruction of charged tracks in GRAIN LAr detector equipped with these cameras will be presented. In particular, the development of key enabling technologies, such as a large, low power cryogenic ASIC and VUV-enhanced Backside Illuminated SiPMs will be emphasized.