Status and Sensitivity Projections for the XENON100 Dark Matter Experiment

TL;DR

The paper presents the XENON100 detector as a 100 kg-scale, two-phase xenon TPC designed to search for WIMPs via spin-independent interactions, with strong S1/S2 discrimination and fiducialization to suppress backgrounds. It details the detector construction, xenon handling and Kr purification, electronics/DAQ, initial commissioning results, and a planned upgrade (QUPID sensors, copper cryostat, extended drift, and a muon veto) to further reduce backgrounds. Background modeling combines measured material radioactivities with Geant4 simulations, predicting low ER and NR backgrounds and enabling a staged WIMP search strategy. The projected sensitivities reach $\sigma_{\chi-p} \sim 6\times10^{-45}$ cm$^2$ (40 days), $\sim 2\times10^{-45}$ cm$^2$ (hundreds of days), and $\sim 2\times10^{-46}$ cm$^2$ for the upgraded 6000 kg-day exposure, significantly probing SUSY and other beyond-standard-model dark matter scenarios, and informing the path toward XENON1T.

Abstract

The XENON experimental program aims to detect cold dark matter particles via their elastic collisions with xenon nuclei in two-phase time projection chambers (TPCs). We are currently testing a new TPC at the 100 kg scale, XENON100. This new, ultra-low background detector, has a total of 170 kg of xenon (65 kg in the target region and 105 kg in the active shield). It has been installed at the Gran Sasso Underground Laboratory and is currently in commissioning phase. We review the design and performance of the detector and its associated systems, present status, preliminary calibration results, background prediction and projected sensitivity. With a 6000 kg-day background-free exposure, XENON100 will reach a sensitivity to spin-independent WIMP-nucleon cross section of 2e-45 cm2 by the end of 2009. We also discuss our plan to upgrade the XENON100 experiment to improve the sensitivity by another order of magnitude by 2012.

Figures (9)

• Figure 1: Spin-independent (left) and spin-dependent pure neutron (right) WIMP-nucleon cross sections as a function of WIMP mass, probed by different stages of the XENON program. On the left, the low mass WIMP region allowed by DAMA Bernabei:2008yi is taken from Savage:2008er, and the current most stringent limits from XENON10 Angle:2007uj and CDMS Ahmed:2008eu are shown as solid curves. The blue shaded regions show the theoretical expectations within the CMSSM Roszkowski:2007fd.
• Figure 2: Schematic view (left) and a picture (right) of the XENON100 time projection chamber.
• Figure 3: Picture of the Kr distillation column during its commissioning at LNGS.
• Figure 4: (Left) The measured scintillation light spectrum based on S1 signals from $^{137}$Cs. (Right) Current and projected goal of the S1 light yield by increasing the LXe purity in XENON100.
• Figure 5: (Left) A typical event waveform from XENON100, showing both S1 and S2 signals. (Right) S2 hit pattern on the top PMT array for the same event.