Dark Matter Results from 225 Live Days of XENON100 Data

TL;DR

A search for particle dark matter with the XENON100 experiment, operated at the Laboratori Nazionali del Gran Sasso for 13 months during 2011 and 2012, has yielded no evidence for dark matter interactions.

Abstract

We report on a search for particle dark matter with the XENON100 experiment, operated at the Laboratori Nazionali del Gran Sasso (LNGS) for 13 months during 2011 and 2012. XENON100 features an ultra-low electromagnetic background of (5.3 \pm 0.6) \times 10^-3 events (kg day keVee)^-1 in the energy region of interest. A blind analysis of 224.6 live days \times 34 kg exposure has yielded no evidence for dark matter interactions. The two candidate events observed in the pre-defined nuclear recoil energy range of 6.6-30.5 keVnr are consistent with the background expectation of (1.0 \pm 0.2) events. A Profile Likelihood analysis using a 6.6-43.3 keVnr energy range sets the most stringent limit on the spin-independent elastic WIMP-nucleon scattering cross section for WIMP masses above 8 GeV/c^2, with a minimum of 2 \times 10^-45 cm^2 at 55 GeV/c^2 and 90% confidence level.

Figures (3)

• Figure 1: Combined cut acceptance (solid blue). The S2 threshold cut S2$>$150 PE (dashed red) is independent of possible fluctuations in S1 and has to be applied to the S1 spectrum before taking into account the S1 resolution. It is conservatively set to zero below 1 PE. For the cross-check with the maximum gap method Yellin:2002xd, a hard discrimination cut is used. Its acceptance to NRs is shown by the dotted green line. The lower analysis threshold is 6.6 keV$_{\mathrm{nr}}$ (3 PE) and extends to 43.3 keV$_{\mathrm{nr}}$, whereas the cross-check is restricted to 30.5 keV$_{\mathrm{nr}}$ (dashed and dotted black lines).
• Figure 2: (Top) Event distribution in the discrimination parameter space $\log_{10}$(S2$_b$/S1), flattened by subtracting the distribution's mean, as observed after unblinding using all analysis cuts and a 34 kg fiducial volume (black squares). A lower analysis threshold of 6.6 keV$_{\mathrm{nr}}$ (NR equivalent energy scale) is employed. The PL analysis uses an upper energy threshold of 43.3 keV$_{\mathrm{nr}}$ (3-30 PE) and the benchmark WIMP search region is limited to 30.5 keV$_{\mathrm{nr}}$ (3-20 PE). The negligible impact of the S2$>$150 PE threshold cut is indicated by the dashed-dotted blue line and the signal region is restricted by a lower border running along the $97\%$ NR quantile. An additional hard S2$_b$/S1 discrimination cut at 99.75% ER rejection defines the benchmark WIMP search region from above (dotted green) but is only used to cross check the PL inference. The histogram in red/gray indicates the NR band from the neutron calibration. Two events fall into the benchmark region where $(1.0 \pm 0.2)$ are expected from background. (Bottom) Spatial event distribution inside the TPC using a 6.6-43.3 keV$_{\mathrm{nr}}$ energy window. The 34 kg fiducial volume is indicated by the red dashed line. Gray points are above the 99.75% rejection line, black circles fall below.
• Figure 3: Result on spin-independent WIMP-nucleon scattering from XENON100: The expected sensitivity of this run is shown by the green/yellow band ($1\sigma/2\sigma)$ and the resulting exclusion limit (90% CL) in blue. For comparison, other experimental limits (90% CL) and detection claims ($2\sigma$) are also shown Savage:2008erAalseth:2010vxAngloher:2011uuAhmed:2009zw, together with the regions ($1\sigma$/$2\sigma$) preferred by supersymmetric (CMSSM) models ref::susymodels.