Limits on Spin-Dependent WIMP-Nucleon Cross Sections from the XENON10 Experiment

XENON10 is an experiment to directly detect weakly interacting massive particles (WIMPs), which may comprise the bulk of the nonbaryonic dark matter in our Universe. We report new results for spin-dependent WIMP-nucleon interactions with ${}^{129}\mathrm{Xe}$ and ${}^{131}\mathrm{Xe}$ from 58.6 live days of operation at the Laboratori Nazionali del Gran Sasso. Based on the nonobservation of a WIMP signal in 5.4 kg of fiducial liquid xenon mass, we exclude previously unexplored regions in the theoretically allowed parameter space for neutralinos. We also exclude a heavy Majorana neutrino with a mass in the range of $\sim 10\mathrm{GeV}/c^2–2\mathrm{TeV}/c^2$ as a dark matter candidate under standard assumptions for its density and distribution in the galactic halo.

Figure 1

XENON10 combined 90% C.L. exclusion limits for ${}^{129}\mathrm{Xe}$ and ${}^{131}\mathrm{Xe}$ for pure-neutron (left) and pure-proton (right) couplings (solid curves). The dashed curves show the combined Xe limits using the alternate form factor. Also shown are the results from the CDMS experiment [20] (diamonds), ZEPLIN-II [21] (circles), KIMS [22] (triangles), NAIAD [23] (squares), PICASSO [24] (stars), COUPP [25] (pluses), SuperK [26] (crosses), as well as the DAMA evidence region under the assumption of standard WIMP nuclear recoils and dark halo parameters (narrow green filled region) [18]. The theoretical regions (blue filled regions below the limit curves) for the neutralino (in the constrained minimal supersymmetric model) are taken from [27].

Figure 2

Left: Predicted number of events in XENON10 for a heavy Majorana neutrino with standard weak interaction as a function of the neutrino mass, using the main (solid curve) and alternate (dashed curve) form factors. The light shaded area shows the excluded mass region at 90% C.L., calculated with Yellin’s maximal gap method [19] for the main form factors. Right: Regions allowed at the 90% C.L. in $a_n-a_p$ parameter space for a WIMP mass of $50\mathrm{GeV}/c^2$. The combined limit from ${}^{129}\mathrm{Xe}$ and ${}^{131}\mathrm{Xe}$ is shown as a dark solid curve (using the main form factor, see text), The exteriors of the corresponding ellipses are excluded, the common space inside the ellipses being allowed by the data. We also show the results obtained by KIMS [22] (dot-dashed line), COUPP [25] (dotted line) (“horizontal” ellipses), and CDMS [20] (dotted line), ZEPLIN-II [21] (dashed line), and the DAMA evidence region [18] (light filled region) (“vertical” ellipses).