Scintillation efficiency and ionization yield of liquid xenon for monoenergetic nuclear recoils down to 4 keV

Liquid xenon (LXe) is an excellent material for experiments designed to detect dark matter in the form of weakly interacting massive particles (WIMPs). A low energy detection threshold is essential for a sensitive WIMP search. The understanding of the relative scintillation efficiency (${\mathcal{L}}_{\mathrm{eff}}$) and ionization yield of low energy nuclear recoils in LXe is limited for energies below 10 keV. In this article, we present new measurements that extend the energy down to 4 keV, finding that ${\mathcal{L}}_{\mathrm{eff}}$ decreases with decreasing energy. We also measure the quenching of scintillation efficiency caused by the electric field in LXe, finding no significant field dependence.