On the spin-dependent sensitivity of XENON100

TL;DR

This paper highlights the strong spin-dependent sensitivity of XENON100 data, especially for neutron interactions, and discusses its implications for dark matter models and future experiments.

Contribution

It demonstrates that XENON100 provides the best current constraints on spin-dependent neutron cross-sections and analyzes nuclear uncertainties affecting these limits.

Findings

XENON100's spin-dependent neutron limits are the most stringent to date.

Nuclear uncertainties impact the robustness of spin-dependent proton constraints.

Future experiments like XENON1T and DARWIN have promising prospects for spin-dependent dark matter detection.

Abstract

The latest XENON100 data severely constrains dark matter elastic scattering off nuclei, leading to impressive upper limits on the spin-independent cross-section. The main goal of this paper is to stress that the same data set has also an excellent \emph{spin-dependent} sensitivity, which is of utmost importance in probing dark matter models. We show in particular that the constraints set by XENON100 on the spin-dependent neutron cross-section are by far the best at present, whereas the corresponding spin-dependent proton limits lag behind other direct detection results. The effect of nuclear uncertainties on the structure functions of xenon isotopes is analysed in detail and found to lessen the robustness of the constraints, especially for spin-dependent proton couplings. Notwithstanding, the spin-dependent neutron prospects for XENON1T and DARWIN are very encouraging. We apply our constraints to well-motivated dark matter models and demonstrate that in both mass-degenerate scenarios and the minimal supersymmetric standard model the spin-dependent neutron limits can actually override the spin-independent limits. This opens the possibility of probing additional unexplored regions of the dark matter parameter space with the next generation of ton-scale direct detection experiments.