Calibration of the liquid argon ionization response to low energy electronic and nuclear recoils with DarkSide-50

Abstract

DarkSide-50 has demonstrated the high potential of dual-phase liquid argon time projection chambers in exploring interactions of WIMPs in the GeV/c${}^2$ mass range. The technique, based on the detection of the ionization signal amplified via electroluminescence in the gas phase, allows to explore recoil energies down to the sub-keV range. We report here on the DarkSide-50 measurement of the ionization yield of electronic recoils down to $\sim$180~eV${}_{er}$, exploiting ${}^{37}$Ar and ${}^{39}$Ar decays, and extrapolated to a few ionization electrons with the Thomas-Imel box model. Moreover, we present a model-dependent determination of the ionization response to nuclear recoils down to $\sim$500~eV${}_{nr}$, the lowest ever achieved in liquid argon, using \textit{in situ} neutron calibration sources and external datasets from neutron beam experiments.

11 pages, 12 figures, 1 table