  Uncertainty in the local dark matter velocity distribution is a key
difficulty in the analysis of data from direct detection experiments. Here we
propose a new approach for dealing with this uncertainty, which does not
involve any assumptions about the structure of the dark matter halo. Given a
dark matter model, our method yields the velocity distribution which best
describes a set of direct detection data as a finite sum of streams with
optimised speeds and densities. The method is conceptually simple and
numerically very efficient. We give an explicit example in which the method is
applied to determining the ratio of proton to neutron couplings of dark matter
from a hypothetical set of future data.
