Limits on spin-dependent WIMP-nucleon cross section obtained from the complete LUX exposure (1705.03380v2)

Abstract: We present experimental constraints on the spin-dependent WIMP-nucleon elastic cross sections from the total 129.5 kg-year exposure acquired by the Large Underground Xenon experiment (LUX), operating at the Sanford Underground Research Facility in Lead, South Dakota (USA). A profile likelihood ratio analysis allows 90% CL upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of $\sigma_n$ = 1.6$\times 10^{-41}$ cm$^{2}$ ($\sigma_p$ = 5$\times 10^{-40}$ cm$^{2}$) at 35 GeV$c^{-2}$, almost a sixfold improvement over the previous LUX spin-dependent results. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.

• The paper presents a comprehensive analysis of spin-dependent WIMP-nucleon interactions using LUX's complete 129.5 kg-year dataset.
• The researchers employed a dual-phase xenon time projection chamber and profile likelihood analysis to derive robust 90% confidence level upper limits.
• The results improve sensitivity nearly sixfold over previous efforts, providing critical constraints for dark matter models and guiding future search experiments.

Analysis of Spin-dependent WIMP-nucleon Cross Section Limits from LUX Data

The paper "Limits on spin-dependent WIMP-nucleon cross section obtained from the complete LUX exposure" presents significant findings from the Large Underground Xenon (LUX) experiment regarding the interaction cross sections between weakly interacting massive particles (WIMPs) and nucleons, specifically focusing on the spin-dependent (SD) interaction channels. This analysis utilized the entirety of LUX's operational data, spanning a total exposure period amounting to 129.5 kg-years, which represents a robust dataset for such detection experiments.

The focus of the paper is on setting constraints on the cross sections for WIMP-neutron and WIMP-proton interactions. The LUX experiment employed a dual-phase xenon time projection chamber to detect potential WIMP interactions by observing the scattering of galactic WIMPs with xenon nuclei. This detection approach enables the experiment to discern between nuclear recoils (indicative of WIMP interactions) and electron recoils (background noise), thus facilitating a clearer observation of potential WIMP-induced events.

Utilizing a sophisticated profile likelihood ratio analysis, the researchers derived 90% confidence level (CL) upper limits, improving by almost sixfold over past efforts. Specifically, the paper places the upper limit for the WIMP-neutron cross section at $1.6 \times 10^{-41} \, \text{cm}^2$ at a WIMP mass of 35 GeV/c$^2$. This establishes LUX's findings as the most sensitive limits to date for this interaction channel. The implications of these limits are notable, particularly regarding their sensitivity to neutron-only coupling scenarios compared to proton-only scenarios, due to the natural isotopic abundance of xenon, which favors neutron interactions given the unpaired neutrons in $^{129}$Xe and $^{131}$Xe.

The broader impact of these results lies in their implications for understanding the nature of dark matter, further constraining theoretical models such as supersymmetry and other beyond-the-Standard-Model hypotheses that propose WIMPs as potential dark matter candidates. Additionally, these results offer complementary constraints to those derived from particle accelerator experiments such as the LHC, particularly in situations where direct and indirect detection efforts intersect.

Looking forward, the LUX team's methodology and enhanced sensitivity serve as a stepping stone for future dark matter search initiatives. Advancing beyond current constraints, experiments could incorporate greater exposure durations, refined detection technology, and complementary investigation channels, thereby improving sensitivity to an array of possible interaction types within the WIMP hypothesis framework. This continued refinement is crucial to either observing these elusive particles or further narrowing the parameter space in which WIMPs might exist, thereby guiding theoretical development in astroparticle physics.

In summary, the paper delivers comprehensive constraints on SD WIMP-nucleon interactions with enhanced sensitivity over previous results, providing a critical piece to the puzzle of dark matter characterization and continuing the progress in particle astrophysics.