  Forecasting the signal discrimination power of dark matter (DM) searches is
commonly limited to a set of arbitrary benchmark points. We introduce new
methods for benchmark-free forecasting that instead allow an exhaustive
exploration and visualization of the phenomenological distinctiveness of DM
models, based on standard hypothesis testing. Using this method, we reassess
the signal discrimination power of future liquid Xenon and Argon direct DM
searches. We quantify the parameter regions where various non-relativistic
effective operators, millicharged DM, and magnetic dipole DM can be
discriminated, and where upper limits on the DM mass can be found. We find that
including an Argon target substantially improves the prospects for
reconstructing the DM properties. We also show that only in a small region with
DM masses in the range 20-100 GeV and DM-nucleon cross sections a factor of a
few below current bounds can near-future Xenon and Argon detectors discriminate
both the DM-nucleon interaction and the DM mass simultaneously. In all other
regions only one or the other can be obtained.
