T. Shutt

Search for light dark matter in XENON10 data.

We report results of a search for light (≲10u2009u2009GeV) particle dark matter with the XENON10 detector. The event trigger was sensitive to a single electron, with the analysis threshold of 5 electrons corresponding to 1.4 keV nuclear recoil energy. Considering spin-independent dark matter-nucleon scattering, we exclude cross sections σ(n)>7×10(-42)u2009u2009cm(2), for a dark matter particle mass m(χ)=7u2009u2009GeV. We find that our data strongly constrain recent elastic dark matter interpretations of excess low-energy events observed by CoGeNT and CRESST-II, as well as the DAMA annual modulation signal.

The Large Underground Xenon (LUX) Experiment

The Large Underground Xenon (LUX) collaboration has designed and constructed a dual-phase xenon detector, in order to conduct a search for Weakly Interacting Massive Particles (WIMPs), a leading dark matter candidate. The goal of the LUX detector is to clearly detect (or exclude) WIMPS with a spin independent cross-section per nucleon of 2×10-46cm2, equivalent to ∼1event/100kg/month in the inner 100-kg fiducial volume (FV) of the 370-kg detector. The overall background goals are set to have <1 background events characterized as possible WIMPs in the FV in 300 days of running. This paper describes the design and construction of the LUX detector.

Limits on spin-dependent WIMP-nucleon cross-sections from the XENON10 experiment

XENON10 is an experiment to directly detect weakly interacting massive particles (WIMPs), which may comprise the bulk of the nonbaryonic dark matter in our Universe. We report new results for spin-dependent WIMP-nucleon interactions with 129Xe and 131Xe from 58.6 live days of operation at the Laboratori Nazionali del Gran Sasso. Based on the nonobservation of a WIMP signal in 5.4 kg of fiducial liquid xenon mass, we exclude previously unexplored regions in the theoretically allowed parameter space for neutralinos. We also exclude a heavy Majorana neutrino with a mass in the range of approximately 10 GeV/c2-2 TeV/c2 as a dark matter candidate under standard assumptions for its density and distribution in the galactic halo.

Constraints on inelastic dark matter from XENON10

It has been suggested that dark matter particles which scatter inelastically from detector target nuclei could explain the apparent incompatibility of the DAMA modulation signal (interpreted as evidence for particle dark matter) with the null results from CDMS-II and XENON10. Among the predictions of inelastically interacting dark matter are a suppression of low-energy events, and a population of nuclear recoil events at higher nuclear recoil equivalent energies. This is in stark contrast to the well-known expectation of a falling exponential spectrum for the case of elastic interactions. We present a new analysis of XENON10 dark matter search data extending to E{sub nr} = 75 keV nuclear recoil equivalent energy. Our results exclude a significant region of previously allowed parameter space in the model of inelastically interacting dark matter. In particular, it is found that dark matter particle masses m{sub x} {approx}> 150 GeV are disfavored.

Simultaneous measurement of ionization and scintillation from nuclear recoils in liquid xenon for a dark matter experiment.

We report the first measurements of the absolute ionization yield of nuclear recoils in liquid xenon, as a function of energy and electric field. Independent experiments were carried out with two dual-phase time-projection chamber prototypes, developed for the XENON dark matter project. We find that the charge yield increases with decreasing recoil energy, and exhibits only a weak field dependence. These results are the first unambiguous demonstration of the capability of dual-phase xenon detectors to discriminate between electron and nuclear recoils down to 20 keV, a key requirement for a sensitive dark matter search.

Design and performance of the XENON10 dark matter experiment

Abstract XENON10 is the first two-phase xenon time projection chamber (TPC) developed within the XENON dark matter search program. The TPC, with an active liquid xenon (LXe) mass of about 14xa0kg, was installed at the Gran Sasso Underground Laboratory (LNGS) in Italy, and operated for more than one year, with excellent stability and performance. Results from a dark matter search with XENON10 have been published elsewhere. In this paper, we summarize the design and performance of the detector and its subsystems, based on calibration data using sources of gamma-rays and neutrons as well as background and Monte Carlo simulation data. The results on the detector’s energy threshold, position resolution, and overall efficiency show a performance that exceeds design specifications, in view of the very low energy threshold achieved (

Radiogenic and Muon-Induced Backgrounds in the LUX Dark Matter Detector

Abstract The Large Underground Xenon (LUX) dark matter experiment aims to detect rare low-energy interactions from Weakly Interacting Massive Particles (WIMPs). The radiogenic backgrounds in the LUX detector have been measured and compared with Monte Carlo simulation. Measurements of LUX high-energy data have provided direct constraints on all background sources contributing to the background model. The expected background rate from the background model for the 85.3xa0day WIMP search run is ( 2.6 ± 0.2 stat ± 0.4 sys ) × 10 - 3 events keV ee - 1 kg - 1 day - 1 in a 118xa0kg fiducial volume. The observed background rate is ( 3.6 ± 0.4 stat ) × 10 - 3 events keV ee - 1 kg - 1 day - 1 , consistent with model projections. The expectation for the radiogenic background in a subsequent one-year run is presented.

Technical results from the surface run of the LUX dark matter experiment

Abstract We present the results of the three-month above-ground commissioning run of the Large Underground Xenon (LUX) experiment at the Sanford Underground Research Facility located in Lead, South Dakota, USA. LUX is a 370xa0kg liquid xenon detector that will search for cold dark matter in the form of Weakly Interacting Massive Particles (WIMPs). The commissioning run, conducted with the detector immersed in a water tank, validated the integration of the various sub-systems in preparation for the underground deployment. Using the data collected, we report excellent light collection properties, achieving 8.4 photoelectrons per keV for 662xa0keV electron recoils without an applied electric field, measured in the center of the WIMP target. We also find good energy and position resolution in relatively high-energy interactions from a variety of internal and external sources. Finally, we have used the commissioning data to tune the optical properties of our simulation and report updated sensitivity projections for spin-independent WIMP-nucleon scattering.

The scintillation and ionization yield of liquid xenon for nuclear recoils

XENON10 is an experiment designed to directly detect particle dark matter. It is a dual phase (liquid/gas) xenon time-projection chamber with 3D position imaging. Particle interactions generate a primary scintillation signal (S1) and ionization signal (S2), which are both functions of the deposited recoil energy and the incident particle type. We present a new precision measurement of the relative scintillation yield View the MathML source and the absolute ionization yield View the MathML source, for nuclear recoils in xenon. A dark matter particle is expected to deposit energy by scattering from a xenon nucleus. Knowledge of View the MathML source is therefore crucial for establishing the energy threshold of the experiment; this in turn determines the sensitivity to particle dark matter. Our View the MathML source measurement is in agreement with recent theoretical predictions above 15 keV nuclear recoil energy, and the energy threshold of the measurement is View the MathML source. A knowledge of the ionization yield View the MathML source is necessary to establish the trigger threshold of the experiment. The ionization yield View the MathML source is measured in two ways, both in agreement with previous measurements and with a factor of 10 lower energy threshold.

The LUX dark matter search

The Large Underground Xenon (LUX) experiment is a liquid xenon time projection chamber designed for extremely low levels of radioactive background in its fiducial volume. The overall liquid xenon mass is 300 kg, with a 100 kg fiducial mass. LUX is currently under construction, and integration of the full detector will begin in Fall 2009 at the Sanford Underground Science and Engineering Laboratory in South Dakota. The LUX sensitivity to the WIMP-nucleon spin-independent scattering cross-section will be 7 × 10-46 cm2 at 100 GeV after 300 days of low-background operation.