Liquified noble gases are widely used as a target in direct Dark Mattersearches. Signals from scintillation in the liquid, following energy depositionfrom the recoil nuclei scattered by Dark Matter particles (e.g. WIMPs), shouldbe recorded down to very low energies by photosensors suitably designed tooperate at cryogenic temperatures. Liquid Argon based detectors for Dark Mattersearches currently implement photo multiplier tubes for signal read-out. In thelast few years PMTs with photocathodes operating down to liquid Argontemperatures (87 K) have been specially developed with increasing QuantumEfficiency characteristics. The most recent of these, Hamamatsu Photonics Mod.R11065 with peak QE up to about 35%, has been extensively tested within the R&Dprogram of the WArP Collaboration. During these testes the Hamamatsu PMTsshowed superb performance and allowed obtaining a light yield around 7phel/keVee in a Liquid Argon detector with a photocathodic coverage in the 12%range, sufficient for detection of events down to few keVee of energydeposition. This shows that this new type of PMT is suited for experimentalapplications, in particular for new direct Dark Matter searches with LAr-basedexperiments.
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