Scintillation and Ionization Responses of Liquid Xenon to Low Energy Electronic and Nuclear Recoils at Drift Fields from 236 V/cm to 3.93 kV/cm

We present new measurements of the scintillation and ionization yields in liquid xenon for low energy electronic (about 3--7 keV$_{ee}$) and nuclear recoils (about 8--20 keV$_{nr}$) at different drift fields from 236 V/cm to 3.93 kV/cm, using a three-dimensional sensitive liquid xenon time projection chamber with high energy and position resolutions. Our measurement of signal responses to nuclear recoils agrees with predictions from the NEST model. However, our measured ionization (scintillation) yields for electronic recoils are consistently higher (lower) than those from the NEST model by about 5 e$^-$/keV$_{ee}$ (ph/keV$_{ee}$) at all scanned drift fields. New recombination parameters based on the Thomas-Imel box model are derived from our data. Given the lack of precise measurement of scintillation and ionization yields for low energy electronic recoils in liquid xenon previously, our new measurement provides so far the best available data covering low energy region at different drift fields for liquid xenon detectors relevant to dark matter searches.

High Resolution Gamma Ray Detection in a Dual Phase Xenon Time Projection Chamber

Dual phase Xenon Time Projection Chambers (XeTPCs) are being used by several experiments as a promising technique for direct detection of dark matter. We report on the design and performance of a small 3-D sensitive dual phase XeTPC. The position resolution is 2 mm in the center of detector, limited by the hole size of the mesh at the proportional scintillation region. An energy resolution of 1.6%({sigma} /E) for 662 keV gamma rays is achieved by combining the ionization and scintillation signals at a drift field of 0.5 kV/cm. This represents the best energy resolution achieved among liquid xenon detectors. The energy resolution is only slightly dependent on drift field. Better than 2% energy resolution ({sigma} /E) for 662 keV gamma rays can be achieved for drift fields between 100 V/cm and 2 kV/cm. With high position and energy resolutions, a dual phase XeTPC has also potential applications in surveys for neutrinoless double-beta decay and in gamma ray imaging.