Limits on Spin-independent Couplings of Light Dark Matter WIMPs with a p-type Point-contact Germanium Detector

New limits on spin-independent WIMP-nucleon coupling using 39.5 kg-days of data taken with a p-type point-contact germanium detector with fiducial mass of 840g at the Kuo-Sheng Reactor Neutrino Laboratory (KSNL) is presented. Charactering and understanding the anomalous surface behaviour is of particular significance to this study. The slow rise-time of surface events is identified via software pulse shape analysis techniques. In addition, the signal-retaining and background-rejecting efficiencies are implied to clarify the actual bulk and surface events in the mixed regime at sub-keV range. Both efficiencies are evaluated with calibration sources and a novel n-type point-contact germanium detector. Efficiencies-corrected background spectra from the low-background facility at KSNL are derived. Part of the parameter space in cross-section versus WIMP-mass is probed and excluded.