Light yield in DarkSide-10: A prototype two-phase argon TPC for dark matter searches

As part of the DarkSide program of direct dark matter searches using two-phase argon TPCs, a prototype detector with an active volume containing 10 kg of liquid argon, DarkSide-10, was built and operated underground in the Gran Sasso National Laboratory in Italy. A critically important parameter for such devices is the scintillation light yield, as photon statistics limits the rejection of electron-recoil backgrounds by pulse shape discrimination. We have measured the light yield of DarkSide-10 using the readily-identifiable full-absorption peaks from gamma ray sources combined with single-photoelectron calibrations using low-occupancy laser pulses. For gamma lines of energies in the range 122-1275 keV, we get light yields averaging 8.887 +/- 0.003(stat)+/- 0.444(sys) p.e./keV(ee). With additional purification, the light yield measured at 511 key increased to 9.142 +/- 0.006(stat) p.e./keV(ee). Published by Elsevier B.V