Speaker
Description
Dual-phase liquid argon time projection chambers (LAr TPCs) are widely used in the direct
search for weakly interacting massive particles (WIMPs), traditionally targeting masses of
the order of 100 GeV. Future-generation LAr TPCs aim to extend this search towards lower
WIMP masses, down to the GeV scale. In this regime, WIMP interactions are expected to
produce nuclear recoils (NRs) in liquid argon with energies of only a few keV, where the
detector response is still not fully characterized.
To address this challenge, the Recoil Directionality (ReD) experiment was developed within
the DarkSide-20k Collaboration to produce and characterize few-keV nuclear recoils in liquid
argon. A compact dual-phase LAr TPC was irradiated with neutrons from a 252Cf source,
producing argon nuclear recoils through neutron scattering. A downstream spectrometer
consisting of 18 plastic scintillators detected neutrons scattered by argon nuclei, enabling
the recoil energy to be reconstructed through two-body kinematics. This technique allowed
the ionization yield of liquid argon, Q_y, defined as the number of electrons produced per
unit energy deposition, to be measured in a model-independent manner down to 2 keV.
The measured Q_y is found to be consistent with existing measurements at higher recoil
energies, while showing an increase towards lower energies. These results provide new
experimental constraints on the modeling of low-energy nuclear recoils in liquid argon and
are particularly relevant for the interpretation of Dark Matter searches in the low-mass WIMP
regime.
In this contribution, an overview of the ReD experiment and its measurement technique will
be presented, together with the main results of the published measurement. Finally, the
impact of the improved characterization of the argon response on the sensitivity of the
upcoming DarkSide-20k experiment will be discussed, highlighting the enhanced discovery
potential for low-mass Dark Matter candidates.
