Abstract
We report the first results of DarkSide-50, a direct search for dark matter operating in the underground Laboratori Nazionali del Gran Sasso (LNGS) and searching for the rare nuclear recoils possibly induced by weakly interacting massive particles (WIMPs). The dark matter detector is a Liquid Argon Time Projection Chamber with a (46.4±0.7) kg active mass, operated inside a 30 t organic liquid scintillator neutron veto, which is in turn installed at the center of a 1 kt water Cherenkov veto for the residual flux of cosmic rays. We report here the null results of a dark matter search for a (1422±67) kgd exposure with an atmospheric argon fill. This is the most sensitive dark matter search performed with an argon target, corresponding to a 90% CL upper limit on the WIMP-nucleon spin-independent cross section of 6.1×10−44 cm2 for a WIMP mass of 100 Gev/c2.
Highlights
The matter content of the universe appears to be dominated not by ordinary baryonic matter but by a non-luminous and nonbaryonic component: dark matter
This paper reports the first physics data from the DarkSide-50 Liquid Argon Time Projection Chamber (LAr TPC), operated in the Gran Sasso National Laboratory (LNGS) in Italy
Based on the measured upper limit of 39Ar in our UAr, a factor >150 below atmospheric argon [11], the present data contain 39Ar background equivalent to at least 215 000 kg d, or 0.6 t yr, with UAr. None of this background survives into the accepted event sample. This key result directly shows that the 39Ar background in the full DarkSide-50 run with UAr can be suppressed, and supports the claim that the order-of-magnitude larger UAr exposures envisioned for ton-scale LAr TPCs can be free of 39Ar background
Summary
The matter content of the universe appears to be dominated not by ordinary baryonic matter but by a non-luminous and nonbaryonic component: dark matter. None of this background survives into the accepted event sample (see Section 10) This key result directly shows that the 39Ar background in the full DarkSide-50 run with UAr can be suppressed, and supports the claim that the order-of-magnitude larger UAr exposures envisioned for ton-scale LAr TPCs can be free of 39Ar background. During this period, the liquid scintillator veto performance was limited due to the unexpectedly high content of 14C in the trimethyl borate (TMB) that was added as a neutron capture agent. The veto performance has been adequate to measure and suppress the very low rate of neutron-induced events in the present data sample, another key goal of the DarkSide program
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