New Constraints on Xenonphobic Dark Matter from DEAP-3600

The first-year results from DEAP-3600, a single-phase liquid argon direct-detection dark matter experiment, were recently reported. At first sight, they seem to provide no new constraints, as the limit lies well within the region already excluded by three different xenon experiments: LUX, PandaX-II, and XENON1T. We point out, however, that this conclusion is not necessarily true, for it is based on the untested assumption that the dark matter particle couples equally to protons and neutrons. For the more general case of isosping-violating dark matter, we find that there are regions in the parameter space where DEAP-3600 actually provides the most stringent limits on the dark matter-proton spin-independent cross section. Such regions correspond to the so-called Xenonphobic dark matter scenario, for which the neutron-to-proton coupling ratio is close to $-0.7$. Our results seem to signal the beginning of a new era in which the complementarity among different direct detection targets will play a crucial role in the determination of the fundamental properties of the dark matter particle.