Incident Velocity-Recoil Angle Distribution and Angular Recoil-Energy Spectrum of 3-Dimensional WIMP-Nucleus Scattering Events

Abstract: In this paper, as a supplementary of our study on the angular distribution of the recoil flux of WIMP-scattered target nuclei and on that of the WIMP effective scattering velocity distribution, we investigate the scattering probability distribution of the WIMP incident velocity versus the nuclear recoil angle in narrow recoil energy windows for different WIMP masses and target nuclei. Our simulation results show that, not only the velocity distribution of incident halo WIMPs, but also a factor of the recoil angle could affect the scattering probability distribution of the available incident velocity-recoil angle combination in a given recoil energy window. Consequently, the 1-D WIMP "effective" velocity distribution corresponding to the considered narrow energy window would not be consistent with that cut simply from the (generating) velocity distribution of incident halo WIMPs. And its contribution to the differential WIMP-nucleus scattering event rate in the considered energy window could thus not be simply estimated by integrating over the 1-D theoretical velocity distribution (of entire halo WIMPs).