Limits on the spin-dependent WIMP-nucleon cross-sections from the first science run of the ZEPLIN-III experiment

We present new experimental constraints on the WIMP-nucleon spin-dependent elastic cross-sections using data from the first science run of ZEPLIN-III, a two-phase xenon experiment searching for galactic dark matter WIMPs based at the Boulby mine. Analysis of \(\sim\)450 kg\(\cdot\)days fiducial exposure revealed a most likely signal of zero events, leading to a 90%-confidence upper limit on the pure WIMP-neutron cross-section of \(\sigma_n=1.8\times 10^{-2}\) pb at 55 GeV/\(c^2\) WIMP mass. Recent calculations of the nuclear spin structure based on the Bonn CD nucleon-nucleon potential were used for the odd-neutron isotopes \(^{129}\)Xe and \(^{131}\)Xe. These indicate that the sensitivity of xenon targets to the spin-dependent WIMP-proton interaction is much lower than implied by previous calculations, whereas the WIMP-neutron sensitivity is impaired only by a factor of \(\sim\)2.