WIMP-nucleon cross-section results from the second science run of ZEPLIN-III

Abstract

We report experimental upper limits on WIMP-nucleon elastic scattering cross sections from the second science run of ZEPLIN-III at the Boulby Underground Laboratory. A raw fiducial exposure of 1,344 kg·days was accrued over 319 days of continuous operation between June 2010 and May 2011. A total of eight events was observed in the signal acceptance region in the nuclear recoil energy range 7-29 keV, which is compatible with background expectations. This allows the exclusion of the scalar cross-section above 4.8×10 −8 pb near 50 GeV/c 2 WIMP mass with 90% confidence. Combined with data from the first run, this result improves to 3.9×10 −8 pb. The corresponding WIMP-neutron spin-dependent cross-section limit is 8.0×10 −3 pb. The ZEPLIN programme reaches thus its conclusion at Boulby, having deployed and exploited successfully three liquid xenon experiments of increasing reach.

First Results from the LUX Dark Matter Experiment at the Sanford Underground Research Facility

“…NR data are consistent with an energy-dependent, non-monotonic reduced light yield with respect to zero field [30] with a minimum of 0.77 and a maximum of 0.82 in the range 3-25 keV nr [23] (compared with 0.90-0.95 used by previous xenon experiments for significantly higher electric fields [46,50]). This is understood to stem from additional, anti-correlated portioning into the ionization channel.…”

“…The 90% C. L. The LUX 90% confidence limit on the spinindependent elastic WIMP-nucleon cross section (blue), together with the ±1σ variation from repeated trials, where trials fluctuating below the expected number of events for zero BG are forced to 2.3 (blue shaded). We also show Edelweiss II [44] (dark yellow line), CDMS II [45] (green line), ZEPLIN-III [46] (magenta line), CDMSlite [47] (dark green line), XENON10 S2-only [20] (brown line), SIMPLE [48] (light blue line) and XENON100 100 live-day [49] (orange line), and 225 live-day [50] (red line) results. The inset (same axis units) also shows the regions measured from annual modulation in CoGeNT [51] (light red, shaded), along with exclusion limits from low threshold re-analysis of CDMS II data [52] (upper green line), 95% allowed region from CDMS II silicon detectors [53] (green shaded) and centroid (green x), 90% allowed region from CRESST II [54] (yellow shaded) and DAMA/LIBRA allowed region [55] interpreted by [56] (grey shaded).…”

Nuclear structure aspects of spin-independent WIMP scattering off xenon

“…Furthermore, WIMPs interact with quarks, allowing for direct dark matter detection by the observation of the nuclear recoil induced by WIMP scattering off nuclei [3]. Several experiments worldwide are searching for this dark matter signature [4][5][6][7][8][9], but so far no unambiguous detection has been achieved. In addition, WIMPs could also scatter inelastically [10], thereby exciting the nucleus and yielding a different dark matter signal.…”

Direct dark matter searches review

“…The combination of signals used by experiments having produced competitive WIMP limits in the last five years are phonon and ionization (CDMS [10], EDELWEISS [11]), heat and scintillation (CRESST [12]) and ionization and scintillation (LUX [13], XENON [14], ZEPLIN [15]). Alternative electron/ion discrimination techniques involve pulse shape of scintillation signals, applicable for example in liquid argon and neon [16], and in CsI [17].…”