A novel approach to dark matter search based on nanometric emulsions

The most convincing candidate as main constituent of the dark matter in the Universe consists of weakly interacting massive particles (WIMP). WIMPs must be electrically neutral and interact with a very low cross-section (sigma < 10(-40) cm(2)) which makes them detectable in direct searches only through the observation of nuclear recoils induced by the WIMP rare scatterings. In the experiments carried out so far, recoiled nuclei are searched for as a signal over a background produced by Compton electrons and neutron scatterings. Signal found by some experiments have not been confirmed by other techniques. None of these experiments is able to detect the track, typically less than one micron long, of the recoiled nucleus and therefore none is able to directly detect the incoming direction of WIMPs. We propose an R&D program for a new experimental method able to observe the track of the scattered nucleus based on new developments in the nuclear emulsion technique: films with nanometric silver grains, expansion of emulsions and very fast completely automated scanning systems. Nuclear emulsions would act both as the WIMP target and as the tracking detector able to reconstruct the direction of the recoiled nucleus. This unique characteristic would provide a new and unambiguous signature of the presence of the dark matter in our galaxy.