DarkSide-50: A WIMP Search with a Two-phase Argon TPC☆

Abstract DarkSide-50 is a two phase argon TPC for direct dark matter detection which is installed at the Gran Sasso underground laboratory, Italy. DarkSide-50 has a 50-kg active volume and will make use of underground argon low in 39 Ar. The TPC is installed inside an active neutron veto made with boron-loaded high radiopurity liquid scintillator. The neutron veto is installed inside a 1000 m 3 water Cherenkov muon veto. The DarkSide-50 TPC and cryostat are assembled in two radon-free clean rooms to reduce radioactive contaminants. The overall design aims for a background free exposure after selection cuts are applied. The expected sensitivity for WIMP-nucleon cross section is of the order of 10 −45  cm 2 for WIMP masses around 100 GeV/c 2 . The commissioning and performance of the detector are described. Details of the low-radioactivity underground argon and other unique features of the projects are reported.