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 spindependent 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 ± 0.19 kg 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 = 1.31 pb and on neutrons of σn = 21.5 pb 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.  2005 Elsevier B.V. All rights reserved.