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3-Dimensional WIMP Effective Velocity Distribution

Chung-Lin Shan

TL;DR

The paper addresses how the velocity distribution of WIMPs that actually scatter off detector nuclei differs from the overall Galactic halo distribution. It introduces a double Monte Carlo scattering-by-scattering approach to generate incident WIMP velocities, transform them to the laboratory frame, and apply recoil criteria to obtain a mass- and target-dependent 3D effective velocity distribution. The study shows a forward-backward asymmetry arising from the interplay between WIMP flux and nuclear form-factor suppression, with this asymmetry and the angular patterns depending on WIMP mass and target (e.g., light versus heavy nuclei) and displaying annual modulation. These findings have potential implications for directional dark matter detection by refining the expected WIMP-induced recoil signatures and guiding detector design. The framework provides a concrete method to quantify the kinematics of scattering WIMPs beyond the standard halo model.

Abstract

In this talk, I discussed a 3-dimensional "effective" velocity distribution of Weakly Interacting Massive Particles (WIMPs), which, instead of the theoretically predicted velocity distribution of "entire" Galactic Dark Matter particles, describes the actual velocity distribution of WIMPs "scattering off" (specified) target nuclei in an underground detector. Based on numerical results carried out by our double Monte Carlo scattering-by-scattering simulation of 3-dimensional elastic WIMP-nucleus scattering, an (asymmetric) "forward-backward asymmetry" was also demonstrated.

3-Dimensional WIMP Effective Velocity Distribution

TL;DR

The paper addresses how the velocity distribution of WIMPs that actually scatter off detector nuclei differs from the overall Galactic halo distribution. It introduces a double Monte Carlo scattering-by-scattering approach to generate incident WIMP velocities, transform them to the laboratory frame, and apply recoil criteria to obtain a mass- and target-dependent 3D effective velocity distribution. The study shows a forward-backward asymmetry arising from the interplay between WIMP flux and nuclear form-factor suppression, with this asymmetry and the angular patterns depending on WIMP mass and target (e.g., light versus heavy nuclei) and displaying annual modulation. These findings have potential implications for directional dark matter detection by refining the expected WIMP-induced recoil signatures and guiding detector design. The framework provides a concrete method to quantify the kinematics of scattering WIMPs beyond the standard halo model.

Abstract

In this talk, I discussed a 3-dimensional "effective" velocity distribution of Weakly Interacting Massive Particles (WIMPs), which, instead of the theoretically predicted velocity distribution of "entire" Galactic Dark Matter particles, describes the actual velocity distribution of WIMPs "scattering off" (specified) target nuclei in an underground detector. Based on numerical results carried out by our double Monte Carlo scattering-by-scattering simulation of 3-dimensional elastic WIMP-nucleus scattering, an (asymmetric) "forward-backward asymmetry" was also demonstrated.

Paper Structure

This paper contains 3 sections, 3 figures.

Table of Contents

  1. Introduction
  2. 3-D WIMP Galactic effective velocity distribution
  3. Conclusions

Figures (3)

  • Figure 1: The radial (left) and the angular (middle) components as well as the average kinetic energy (right) of the 3-D WIMP Galactic effective velocity distribution. See the text for further details.
  • Figure 2: The radial (a) and the angular (b) components of the 3-D WIMP Galactic effective velocity distribution simulated with 500 total events on average in each 60-day observation period of four advanced seasons DMDDD-NDMDDD-3D-WIMP-N. 200-GeV WIMPs scatter off $\sp{19} {\rm F}$. See the text for further details.
  • Figure 3: The same as Figs. \ref{['fig:N-F19-0200-G-0500-04949']}, except that $\sp{129} {\rm Xe}$ is considered as our target.