http://arxiv.org/abs/1502.04224
Dark matter (DM) direct detection experiments which are directionally-sensitive may be the only method of probing the full velocity distribution function (VDF) of the Galactic DM halo. We present an angular basis for the DM VDF which can be used to parametrise the distribution in order to mitigate astrophysical uncertainties in future directional experiments and extract information about the DM halo. This basis consists of discretising the VDF in a series of angular bins, with the VDF being only a function of the DM speed $v$ within each bin. In contrast to other methods, such as spherical harmonic expansions, the use of this basis allows us to guarantee that the resulting VDF is everywhere positive and therefore physical. We present a recipe for calculating the event rates corresponding to the discrete VDF for an arbitrary number of angular bins $N$ and investigate the discretisation error which is introduced in this way. For smooth, Standard Halo Model-like distribution functions, only $N=3$ angular bins are required to achieve an accuracy of better than $10\%$. For more extreme VDFs (such as streams), the discretisation error is more substantial, but still smaller than the potential error arising from astrophysical uncertainties. This method paves the way towards an astrophysics-independent analysis framework for the directional detection of dark matter.
B. Kavanagh
Tue, 17 Feb 15
33/60
Comments: 32 pages, 10 figures. To be submitted to JCAP. Python code for Radon transform calculation available from the author
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