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 weakly interacting massive particles based at the Boulby mine. Analysis of $\sim 450\mathrm{kg}·\mathrm{days}$ fiducial exposure allow us to place a 90%-confidence upper limit on the pure WIMP-neutron cross section of ${\sigma }_n=1.9\times {10}^{-2}\mathrm{pb}$ at $55\mathrm{GeV}/c^2$ WIMP mass. Recent calculations of the nuclear spin structure based on the Bonn charge-dependent nucleon-nucleon potential were used for the odd-neutron isotopes ${}^{129}\mathrm{Xe}$ and ${}^{131}\mathrm{Xe}$. These indicate that the sensitivity of xenon targets to the spin-dependent WIMP-proton interaction could be much lower than implied by previous calculations, whereas the WIMP-neutron sensitivity is impaired only by a factor of $\sim 2$.

Figure 1

Upper limits on pure WIMP-neutron and WIMP-proton SD cross sections. In addition to ZEPLIN-III with both $NN$ potentials, we show other xenon experiments in black: ZEPLIN-I [23], ZEPLIN-II [24] and XENON10 (Bonn A) [18, 19]. Additional curves are CDMS-II [25], COUPP [26], EDELWEISS [27], KIMS [28], NAIAD [29], PICASSO [30] and SIMPLE [31]. The pure-proton indirect limit from Super-Kamiokande is also shown [32]. The DAMA evidence region interpreted as a nuclear recoil signal in a standard halo [7] is indicated in green. The hatched area is the tip of the 95% probability region for neutralinos in the constrained minimal supersymmetric standard model (CMSSM) [22].

Figure 2

Allowed regions in the $a_n-a_p$ parameter space for 50 GeV WIMP mass.