Xiaonan Li

New limits on spin-independent and spin-dependent couplings of low-mass WIMP dark matter with a germanium detector at a threshold of 220 eV

An energy threshold of (220{+-}10) eV was achieved at an efficiency of 50% with a four-channel ultralow-energy germanium detector, each with an active mass of 5 g. This provides a unique probe to weakly interacting massive particles (WIMP) dark matter with mass below 10 GeV. With a data acquisition live time of 0.338 kg-day at the Kuo-Sheng Laboratory, constraints on WIMPs in the galactic halo were derived. The limits improve over previous results on both spin-independent WIMP-nucleon and spin-dependent WIMP-neutron cross-sections for WIMP mass between 3 and 6 GeV. Sensitivities for full-scale experiments are projected. This detector technique makes the unexplored sub-keV energy window accessible for new neutrino and dark matter experiments.

Prospects of cold dark matter searches with an ultra-low-energy germanium detector

The report describes the research program on the development of ultra-low-energy germanium detectors, with emphasis on WIMP dark matter searches. A threshold of 100 eV is achieved with a 20 g detector array, providing a unique probe to the low-mass WIMP. Present data at a surface laboratory is expected to give rise to comparable sensitivities with the existing limits at the 5 – 10 GeV WIMP-mass range. The projected parameter space to be probed with a full-scale, kilogram mass-range experiment is presented. Such a detector would also allow the studies of neutrino-nucleus coherent scattering and neutrino magnetic moments.