Dark Matter Results from 100 Live Days of XENON100 Data

Abstract: We present results from the direct search for dark matter with the XENON100 detector, installed underground at the Laboratori Nazionali del Gran Sasso of INFN, Italy. XENON100 is a two-phase time projection chamber with a 62 kg liquid xenon target. Interaction vertex reconstruction in three dimensions with millimeter precision allows to select only the innermost 48 kg as ultra-low background fiducial target. In 100.9 live days of data, acquired between January and June 2010, no evidence for dark matter is found. Three candidate events were observed in a pre-defined signal region with an expected background of 1.8 +/- 0.6 events. This leads to the most stringent limit on dark matter interactions today, excluding spin-independent elastic WIMP-nucleon scattering cross-sections above 7.0x10^-45 cm^2 for a WIMP mass of 50 GeV/c^2 at 90% confidence level.

• The paper presents a 100-day study using a liquid xenon detector to search for WIMP-induced nuclear recoils.
• It employs a two-phase time projection chamber with precise 3D event reconstruction to achieve ultra-low background levels.
• Results set a stringent upper limit on the spin-independent WIMP-nucleon cross-section, refining dark matter interaction models.

Dark Matter Results from 100 Live Days of XENON100 Data

The paper presents findings from the XENON100 dark matter experiment, conducted at the Laboratori Nazionali del Gran Sasso in Italy. The primary objective of this experiment is to detect dark matter particles, specifically Weakly Interacting Massive Particles (WIMPs), through their interaction with a 62 kg liquid xenon (LXe) target within a two-phase time projection chamber (TPC). This setup allows for the precise reconstruction of interaction vertices in three dimensions, utilizing the innermost 48 kg as the fiducial target to achieve ultra-low background levels.

Methodology

The XENON100 detector employs a highly purified LXe target, designed to minimize radioactive background interference. Detection relies on capturing both scintillation (S1) and ionization signals (S2) generated by particle interactions. The detector employs a set of photomultiplier tubes (PMTs) to achieve this, optimizing the capacity to discriminate between potential WIMP signals, which are expected to induce nuclear recoils (NRs), and electronic recoils (ERs) caused by environmental background.

The analysis leverages a range of algorithms to evaluate the spatial locations of detected events with high precision, aiming for a millimeter-level resolution. Calibration was conducted with multiple radioactive sources, such as $^{60}$Co and $^{137}$Cs, to ensure accurate mapping of response characteristics within the detector.

Results

Over a span of 100.9 live days, XENON100 observed no significant evidence for dark matter interactions. Within the energy window of interest, three candidate events were identified in the WIMP search region. This is consistent with the anticipated background count of $(1.8 \pm 0.6)$ events. Consequently, a stringent limit was established on the spin-independent WIMP-nucleon scattering cross-section, positioning it below $7.0 \times 10^{-45}$ cm$^2$ for a WIMP mass of 50 GeV/c$^2$ at a 90% confidence level—the most stringent limit at the time of the experiment.

Implications

The implications of these results are substantial for both theoretical and experimental searches for dark matter. By pushing the boundaries of observable parameter space, the XENON100 experiment constrains existing models of WIMP interactions, contributing to the refinement of theoretical frameworks concerning dark matter properties. These findings also put pressure on alternate results, such as those suggested by the DAMA and CoGeNT experiments, which indicated potential signals for light WIMPs.

Future Developments

Moving forward, improvements in detector sensitivity, background discrimination, and technical enhancements will be critical. Future phases of the XENON project as well as other xenon-based or alternative dark matter detection experiments will likely continue to build on these findings, striving to either uncover new evidence of WIMPs or further constrain their interaction cross-sections. Enhanced capabilities to mitigate background interference, alongside expanded xenon targets, could provide stronger insights into the existence and properties of dark matter within the near future.

In summary, the XENON100 experiment provides a crucial contribution to the field of astroparticle physics by setting unprecedented limits on WIMP interactions and guiding subsequent experimental efforts to explore the elusive nature of dark matter.