Probing the Local Velocity Distribution of WIMP Dark Matter with Directional Detectors

TL;DR

This paper investigates how directional detectors can improve understanding of WIMP dark matter velocity distributions, especially in identifying structures like streams or dark disks, through Bayesian analysis of simulated data.

Contribution

It demonstrates the potential of directional detectors combined with energy spectrum data to constrain complex local dark matter velocity structures.

Findings

Directional information helps break degeneracies in velocity distribution parameters.

Cold tidal streams can be well constrained with the proposed setup.

Detecting dark disks with low lag speed is challenging without lower energy thresholds.

Abstract

We explore the ability of directional nuclear-recoil detectors to constrain the local velocity distribution of weakly interacting massive particle (WIMP) dark matter by performing Bayesian parameter estimation on simulated recoil-event data sets. We discuss in detail how directional information, when combined with measurements of the recoil-energy spectrum, helps break degeneracies in the velocity-distribution parameters. We also consider the possibility that velocity structures such as cold tidal streams or a dark disk may also be present in addition to the Galactic halo. Assuming a carbon-tetrafluoride detector with a 30-kg-yr exposure, a 50-GeV WIMP mass, and a WIMP-nucleon spin-dependent cross-section of 0.001 pb, we show that the properties of a cold tidal stream may be well constrained. However, measurement of the parameters of a dark-disk component with a low lag speed of ~50 km/s may be challenging unless energy thresholds are improved.