  The DarkSide-50 direct-detection dark matter experiment is a dual-phase argon
time projection chamber operating at Laboratori Nazionali del Gran Sasso. This
paper reports on the blind analysis of a (16,660+-270) kg d exposure using a
target of low-radioactivity argon extracted from underground sources. We find
no events in the dark matter selection box and set a 90% C.L. upper limit on
the dark matter-nucleon spin-independent cross section of 1.14E-44 cm^2
(3.78E-44 cm^2, 3.43E-43 cm^2) for a WIMP mass of 100 GeV/c^2 (1 TeV/c^2, 10
TeV/c^2).
