Measurement of the nuclear recoil ionization yield in liquid xenon from 0.3 keV to 6 keV

We present a new measurement of the ionization yield in liquid xenon for nuclear recoils between 0.3 - 6 keV, directly targeting the region of interest for low-mass WIMP dark matter and coherent scattering of solar or reactor neutrinos. A collimated, pulsed source of 579 keV neutrons was generated via the Li(p,n)Be reaction using the tandem accelerator at Triangle Universities Nuclear Laboratory. Neutrons scattering elastically in the xenon target were tagged by liquid scintillator detectors at fixed angles between 15 and 70 degrees. Time-of-flight and pulse shape information in the liquid scintillators provide substantial background rejection, allowing us to measure signals with a threshold at a single ionization electron. Data are taken with three different electric fields applied to the liquid target. This is the lowest energy nuclear recoil calibration in liquid xenon reported to date, and can be used to interpret data and compute sensitivities of liquid-xenon-based experiments searching for coherent neutrino-nucleus scattering or low-mass WIMP dark matter.