Reflectance of vacuum ultraviolet-sensitive silicon photomultipliers in liquid xenon

Silicon Photomultiplier (SiPMs) are pixelated semiconductor photosensors with single photon resolution and a strong candidate for the ultimate low light-level detector due to their compact robust geometry, low power consumption, insensitivity to magnetic fields and easy scalability. Vacuum ultraviolet-sensitive SiPMs are innovative SiPM modifications suitable for detecting scintillation photons from liquid noble gases as used in various astroparticle physics detectors e.g. for neutrinoless double beta decay or dark matter searches. SiPMs need to be characterised extensively focussing on their optical and electronic behaviour to determine the SiPM operation parameters which influence the energy resolution of such detectors. Many astroparticle groups plan to use SiPM-based photosensor systems directly within the liquid noble gas detector material so SiPM parameters need to be measured within the same environments for reliable results. We present results from the first reflectance studies with SiPMs in liquid xenon and for vacuum ultraviolet photons. Such reflectance studies are important to determine the angular dependence of the SiPM photon detection efficiency as well as the optical influence of the complex SiPM surface microstructure required for the pixelation of the sensor.