Constraining the Spin-Dependent WIMP-Nucleon Cross Sections with XENON1T

We report the first experimental results on spin-dependent elastic weakly interacting massive particle (WIMP) nucleon scattering from the XENON1T dark matter search experiment. The analysis uses the full ton year exposure of XENON1T to constrain the spin-dependent proton-only and neutron-only cases. No significant signal excess is observed, and a profile likelihood ratio analysis is used to set exclusion limits on the WIMP-nucleon interactions. This includes the most stringent constraint to date on the WIMP-neutron cross section, with a minimum of $6.3\times {10}^{-42}{\mathrm{cm}}^2$ at $30\mathrm{GeV}/c^2$ and 90% confidence level. The results are compared with those from collider searches and used to exclude new parameter space in an isoscalar theory with an axial-vector mediator.

Figure 1

Comparison of the WIMP-nucleus recoil spectra in the SD neutron-only (green), SD proton-only (blue), and SI (orange, scaled by ${10}^{-4}$) cases in LXe for a $10\mathrm{GeV}/c^2$ (solid curve) and $100\mathrm{GeV}/c^2$ (dashed curve) WIMP and a WIMP-nucleon cross section of ${10}^{-45}{\mathrm{cm}}^2$. The bands on the SD spectra come from uncertainties in the contribution to SD scattering from interactions involving the exchange of a pion between two nucleons (two-body currents). The WIMP search region in XENON1T is depicted by the total efficiency curve (gray dotted).

Figure 2

XENON1T 90% C.L. upper limit on the spin-dependent WIMP-neutron cross section from a 1 ton year exposure. The range of expected sensitivity is indicated by the green ($1\sigma$) and yellow ($2\sigma$) bands. Also shown are the experimental results from XENON100 [24], LUX [25], and PandaX-II [26]. We use the “chiral EFT” limit from PandaX-II, since it is based on the same SD interaction model as all other shown results.

Figure 3

XENON1T 90% C.L. upper limit on the spin-dependent WIMP-proton cross section from a 1 ton year exposure. The range of expected sensitivity is indicated by the green ($1\sigma$) and yellow ($2\sigma$) bands. Selected experimental results are shown for XENON100 [24], LUX [25], PandaX-II [26], and PICO-60 [34]. We use the chiral EFT limit from PandaX-II, since it is based on the same SD interaction model as all other shown results.

Figure 4

XENON1T 95% C.L. upper limit in the $m_{\mathrm{med}}–m_{\chi }$ plane for a simplified isoscalar model with an axial-vector mediator and a Dirac WIMP, where the mediator-quark ($g_q$) and mediator-WIMP ($g_{\chi }$) couplings are fixed to 0.25 and 1.0, respectively. Shown for comparison are 95% C.L. limits from PICO-60 [38], ATLAS [40], and CMS [41]. The shaded regions are excluded by the correspondingly colored limits.