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

TL;DR

This paper reports new experimental limits on spin-dependent WIMP-nucleon interactions from the ZEPLIN-III dark matter search, setting upper bounds on the WIMP-neutron cross-section based on zero observed events in a 450 kg·day exposure.

Contribution

It provides the first constraints from ZEPLIN-III on spin-dependent WIMP-nucleon cross-sections using updated nuclear spin structure calculations.

Findings

No events observed in the fiducial volume.

Upper limit on WIMP-neutron cross-section of 1.8×10⁻² pb at 55 GeV/c².

Revised nuclear spin structure calculations reduce sensitivity to WIMP-proton interactions.

Abstract

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.