Michael Wagenpfeil

VUV-sensitive SiPMs for light detection in the nEXO experiment(pdf)

The nEXO experiment will be a 5t LXe TPC for the search for the hypothetical neutrinoless double beta decay of Xe136. The detector will use 4 m² of silicon photomultipliers (SiPM) operated at about -104 C. There are strong demands on xenon purity, radio purity and the SiPM performance to set the most stringent limits on the decay parameters. Detecting the 0vbb-decay would have wide-spread implications for neutrino physics. The SiPMs need to be sensitive to the vacuum-ultraviolet LXe scintillation light (178 nm) which is not given for off-the shelf SiPMs. A decent SiPM performance is required to meet the nEXO requirements, namely a photon detection efficiency of at least 15% @178nm, a correlated avalanche probability of less than 20% and a low dark rate. The VUV-reflectance of the SiPM surface in LXe is an important parameter for light collection efficiency simulations. We present current measurements with state-of-the-art SiPM devices focussing on the PDE and the reflectance.