Angular signatures for galactic halo weakly interacting massive particle scattering in direct detectors: Prospects and challenges - art. no. 043507

Angular sensitivity can provide a key additional tool which might allow una mbiguous separation of a signal due to galactic halo WIMPs from other possi ble backgrounds in direct detectors. We provide a formalism that allows a c alculation of the expected angular distribution of events in terrestrial de tectors with angular sensitivity for any incident distribution of galactic halo dark matter. This can be used as an input when studying the sensitivit y of specific detectors to halo WIMPs. We utilize this formalism to examine the expected signature for WIMP dark; matter using a variety of existing a nalytic halo models in order to explore how uncertainty in the galactic hal o distribution impact on the the event rates that may be required to separa te a possible WIMP signal from terrestrial backgrounds. We find that as few as 30 events might be required to disentangle the signal from backgrounds if the WIMP distribution resembles an isothermal sphere distribution. On th e other hand, for certain halo distributions, even detectors with fine angu lar resolution may require in excess of a 100-400 events to distinguish a W IMP signal from backgrounds using angular sensitivity. We also note that fo r finite thresholds the different energy dependence of spin-dependent scatt ering cross sections may require a greater number of events to discern a WI MP signal than for spin independent interactions. Finally, we briefly descr ibe ongoing studies aimed at developing strategies to better exploit angula r signatures, and the use of N-body simulations to better model the expecte d halo distribution in predicting the expected signature for direct WIMP de tectors.