Discrimination of anisotropy in dark matter velocity distribution with directional detectors

The directional detection of dark matter is sensitive to both recoil energy and the direction of nuclear recoil. It provides a technique whereby the local velocity distribution of dark matter may be measured. In this study, the possibility of discriminating between isotropic and anisotropic distributions is investigated through numerical simulations with a directional detector. The numerical simulation is performed for two cases. These cases are classified according to detectors as follows: one corresponds to an angular histogram distribution of the signals whereas the other corresponds to an energy-angular distribution of the signals. In order to discriminate the energy-angular distributions, a chi-squared test between ideal data set and experimental data and likelihood estimation are proposed. The anisotropy of the velocity distribution was shown to be discriminated at 90% confidence level if O(104) signals are obtained for both gaseous detector and solid detector. Especially, the analysis for the solid detector case and comparison with the gaseous detector case are discussed for the first time.