Results on the Spin-Dependent Scattering of Weakly Interacting Massive Particles on Nucleons from the Run 3 Data of the LUX Experiment (1602.03489v3)

Abstract: We present the first experimental constraints on the spin-dependent WIMP-nucleon elastic cross sections from LUX data acquired in 2013. LUX is a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), which is designed to observe the recoil signature of galactic WIMPs scattering from xenon nuclei. A profile likelihood ratio analysis of $1.4~\times~10^{4}~\text{kg}\cdot~\text{days}$ of fiducial exposure allows 90% CL upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of $\sigma_n~=~9.4~\times~10^{-41}~\text{cm}^2$ ($\sigma_p~=~2.9~\times~10^{-39}~\text{cm}^2$) at 33 GeV/c$^2$. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.

Spin-Dependent Scattering in LUX: Experimental Constraints on WIMP Interactions with Nucleons

The paper presented in the paper "Results on the Spin-Dependent Scattering of Weakly Interacting Massive Particles on Nucleons from the Run 3 Data of the LUX Experiment" provides crucial insights into the elusive interactions of Weakly Interacting Massive Particles (WIMPs) with matter, focusing specifically on spin-dependent scattering. Conducted using the Large Underground Xenon (LUX) detector, a dual-phase xenon time projection chamber, this experiment was set up to detect nuclear recoils resulting from WIMPs as they interact with xenon nuclei.

Experimental Approach and Technical Insights

LUX functions with a 250 kg active xenon mass situated at the Sanford Underground Research Facility. The setup involves detecting scintillation (S1) and ionization (S2) signals produced by recoiling xenon nuclei, which allows precise temporal and spatial calibration for identifying WIMP interactions. The data, recorded over an exposure of 1.4 × 10⁴ kg·days, has undergone rigorous analysis to enhance background model, vertex reconstruction, and event selection processes. This results in an unparalleled sensitivity to WIMP interactions.

The reanalysis of 2013 LUX data refines the understanding of spin-dependent interactions. With a focus beyond the spin-independent (SI) interaction typically enhanced by isospin considerations at the nuclear level, this work distinguishes between WIMP interactions with protons and neutrons. It is important because models propose suppression of the SI interaction or highlight the significance of axial-vector, spin-dependent interactions, making the pursuit of constraints in this area pivotal.

Results and Statistical Inference

The paper advances constraints on spin-dependent WIMP-nucleon interactions by employing a profile likelihood ratio approach across multiple dimensions—S1, S2, radial drift, and vertical position. With observed events aligning with expected backgrounds, the limits on spin-dependent cross sections are markedly improved. Specifically, for WIMP masses around 33 GeV/c², the WIMP-neutron cross section upper limit stands at 9.4 × 10⁻⁴¹ cm², the most sensitive constraint recorded to date. The results represent a substantial leap forward in narrowing down the potential cross-section values, surpassing earlier findings by other direct detection experiments.

Implications and Future Directions

The current work sets the stage for comprehensive constraints on effective WIMP coupling constants ($a_p$, $a_n$), emphasizing the complementarity of various detector materials. The LUX experiment's contributions are particularly valuable in challenging theoretical models that predict distinct interaction profiles within the context of supersymmetric frameworks and beyond. These results also have implications for collider-based dark matter searches, providing a benchmark against which indirect approaches might be contrasted.

Looking ahead, planned advancements with large-scale xenon-based detectors, such as the LZ experiment, promise to amplify sensitivity to both neutron and proton couplings further. This trajectory fortifies ongoing efforts in both direct and indirect investigations of dark matter, enabling a more holistic understanding of potential WIMP structures and interactions.

In summation, the LUX experiment's findings underscore an improved comprehension of WIMP-nucleon scattering, specifically spin-dependent interactions. These results not only provide immediate constraints but also guide future explorations in dark matter research across diversified experimental domains.