First results from the LUX dark matter experiment at the Sanford Underground Research Facility (1310.8214v2)

Abstract: The Large Underground Xenon (LUX) experiment, a dual-phase xenon time-projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), was cooled and filled in February 2013. We report results of the first WIMP search dataset, taken during the period April to August 2013, presenting the analysis of 85.3 live-days of data with a fiducial volume of 118 kg. A profile-likelihood analysis technique shows our data to be consistent with the background-only hypothesis, allowing 90% confidence limits to be set on spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of $7.6 \times 10^{-46}$ cm$^{2}$ at a WIMP mass of 33 GeV/c$^2$. We find that the LUX data are in strong disagreement with low-mass WIMP signal interpretations of the results from several recent direct detection experiments.

• The paper presents the first 85.3-day dataset from LUX, setting a new upper limit of 7.6×10⁻⁴⁶ cm² on the spin-independent WIMP-nucleon cross section for 33 GeV WIMPs.
• It details a dual-phase xenon time-projection chamber methodology that effectively discriminates between nuclear and electron recoils to reduce background noise.
• The findings, though not confirming a WIMP detection, refine dark matter search sensitivity and guide future experimental strategies in direct detection.

Evaluation of the First Results from the LUX Dark Matter Experiment

The Large Underground Xenon (LUX) experiment represents a significant step forward in the search for Weakly Interacting Massive Particles (WIMPs), a leading dark matter candidate. Situated at the Sanford Underground Research Facility, the LUX detector utilizes a liquid xenon target to capture possible interactions between WIMPs and ordinary matter, specifically through nuclear recoil events. The paper presents the inaugural dataset results from an 85.3-day WIMP search period, characterized by rigorous control of background noise and precision in data collection.

Experimental Setup and Methodology

Operating 4850 feet underground, the LUX experiment mitigates cosmic radiation interference using a cylindrical water tank for external shielding. It employs a dual-phase xenon time-projection chamber (TPC), exploiting the properties of both the liquid and gaseous states of xenon for detecting scintillation (S1) and ionization (S2) signals. Photomultiplier tubes (PMTs) track light signals to discern between nuclear recoils (NR) consistent with potential WIMP interactions and electron recoils (ER) predominately from background events.

A critical aspect of the experiment is the profile-likelihood analysis applied to the collected data. This analysis confirmed the data's consistency with a background-only hypothesis, setting stringent upper limits on the spin-independent WIMP-nucleon cross section, reaching a minimum at $7.6 \times 10^{-46} \ \text{cm}^2$ for a WIMP mass of 33 GeV/c². The results significantly differ from other recent experiments suggesting low-mass WIMP signals, thus contributing to the field's ongoing discourse regarding such detections.

Numerical Results and Interpretation

The sensitivity of LUX to spin-independent WIMP cross sections has surpassed previous efforts, demonstrating notable advancements in experimental design and data interpretation. Over the 85.3 live-day span, 160 events were observed within the search criterion of 2-30 photoelectrons for NR signals, consistently matching predicted background levels. This precision underscores the robustness of LUX's background discrimination and detection capabilities.

Theoretical and Practical Implications

The results from the LUX experiment provide critical insights into the dark matter search. While no WIMP detection was confirmed, the experiment establishes a new benchmark in direct detection sensitivity and adds considerable weight to the non-detection results across various WIMP masses. These findings will likely influence theoretical modeling and the calibration of future research efforts, prompting reevaluation of low-mass WIMP interpretations and directing focus towards new detection strategies or alternative dark matter candidates.

Future Prospects

Ongoing and future LUX campaigns aim to extend the dataset to a 300-live-day search, potentially increasing sensitivity to uncharted WIMP parameter space. Improvements in detector operations, including calibration techniques and background reduction mechanisms, are expected to optimize the experiment's performance, fostering advancements in the direct detection of dark matter.

In summary, the LUX experiment's first results are seminal in constraining WIMP models and refining our understanding of dark matter properties. Continued exploration and innovation in detector technology will undoubtedly render further insights and expansive search potential, steering experimental astrophysics towards unraveling the dark matter enigma.