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

TL;DR

This paper reports the first measurements of ionization response in liquid argon for low-energy electronic and nuclear recoils, crucial for dark matter detection, down to unprecedented energy thresholds.

Contribution

It provides new low-energy ionization yield measurements for electronic and nuclear recoils in liquid argon, extending the detection capabilities for dark matter experiments.

Findings

Ionization yield for electronic recoils measured down to 180 eV

Ionization response for nuclear recoils determined down to 500 eV

First-ever low-energy nuclear recoil calibration in liquid argon

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.