Features and performances of the DUNE Far Detectors Photon Detection System

The Photon Detection Systems of the first two Liquid Argon Time Projection Chambers (LArTPCs) of the DUNE Far Detector exploit the Horizontal and Vertical Drift technologies and are composed of 6000 and 672 photon detection units respectively, named X-Arapuca. The Photon Detection Systems will complement and improve the calorimetry and vertex reconstruction for beam events and the prompt light detection will enable the trigger for non-beam events, such as Supernova Neutrino Bursts. In the Horizontal Drift, the Photon Detection System is placed behind the anode planes of the LArTPC, while in the Vertical Drift it is located on the cathode, biased at 320 kV, thus requiring targeted solutions to power and read the X-Arapuca devices. The X-Arapuca is a photon trap with two light downshifting stages, where the light is conveyed to SiPMs with a large area Wavelength Shifting light guide. Its Photon Detection Efficiency, and consequently the Photon Detection Systems sensitivity to the DUNE physics reaches, is determined by the grade and coupling of its several components. The Photon Detection Systems of both Horizontal and Vertical Drift are presented and discussed in their individual features, with a focus on the photon collector components and on the performances achieved by the X-Arapuca units measured in laboratory and in the CERN facilities at the Neutrino Platform. Possible changes in the baseline X-Arapuca designs proposed to further enhance the Photon Detection Efficiency of both Horizontal and Vertical Drift are also discussed. The Horizontal and Vertical Drift scale 1:20 prototypes at the NP04 and NP02 CERN Neutrino Platform, instrumented with the baseline versions of the X-Arapuca, will be operated with Liquid Argon throughout 2024.