Liquid Scintillator Response to Proton Recoils in the 10-100 keV Range

We study the response of EJ-301 liquid scintillator to monochromatic 244.6 $\pm$ 8.4 keV neutrons, targeting the 10-100 keV proton recoil energy interval. Limited experimental information exists for proton light yield in this range, for this or any other organic scintillator. Our results confirm the adequacy of a modified Birks' model, common to all organic scintillator formulations, predicting a marked increase in quenching factor as proton energy approaches the few keV regime. The relevance of this behavior within the context of searches for low-mass particle dark matter is mentioned.