Measurement of liquid argon scintillation and ionization response on nuclear recoils under electric fields up to 3 kV/cm

A liquid argon (LAr) scintillation detector has several features that make it attractive for use in various physics projects such as dark matter searches. One of the key quantities in these projects is the scintillation and ionization response on nuclear recoils (NR) with an energy of several tens of keV and below. The response is known to be dependent on the recoil energy and applied electric field. Although these properties have been measured in previous studies, a systematic understanding and indepth discussions that include low energy and high electric fields have not been conducted. Here, the scintillation and ionization efficiencies of NR with an energy of a few tens of keV under electric fields ranging from 0 to 3 kV/cm are measured. The calibration data are taken with a Cf-252 radioactive neutron source with a small-sized double-phase time projection chamber. We employ a parametrization model to describe the response, and it allows to fully predict the efficiencies at any recoil energy and any electric field below 3 kV/cm.