Discrimination of a small dark matter signal from residual nuclear recoil background by means of two target elements

In planned large dark matter experiments, a small population of nuclear recoils due to dark matter interactions will be difficult to distinguish from a possible residual background of neutron interactions or a low energy alpha background from U/Th in the containing vessel. Simulations are presented which demonstrate this ambiguity for small signals with Poisson fluctuations, and which show the feasibility of resolving this ambiguity in the case of spin-independent weak interactions by comparing signals from two or more target elements with a large difference in A2. Examples are shown for liquid Xe/Ar and gas mixture targets.