Improved spin-dependent limits from the PICASSO dark matter search experiment

The PICASSO experiment reports an improved limit for the existence of cold dark matter WIMPs interacting via spin-dependent interactions with nuclei. The experiment is installed in the Sudbury Neutrino Observatory at a depth of 2070 m. With superheated C4F10 droplets as the active material, and an exposure of 1.98±0.19kg day, no evidence for a WIMP signal was found. For a WIMP mass of 29 GeV/c2, limits on the spin-dependent cross section on protons of σp=1.31pb and on neutrons of σn=21.5pb have been obtained at 90% C.L. In both cases, some new parameter space in the region of WIMP masses below 20 GeV/c2 has now been ruled out. The results of these measurements are also presented in terms of limits on the effective WIMP-proton and neutron coupling strengths ap and an.