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 the determination of the ionization response to nuclear recoils down to \(\sim\)500 eV\(_{nr}\), the lowest ever achieved in liquid argon, using in situ neutron calibration sources and external datasets from neutron beam experiments.