D. N. McKinsey

Search for light dark matter in XENON10 data.

We report results of a search for light (≲10  GeV) 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)  cm(2), for a dark matter particle mass m(χ)=7  GeV. 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.

Consistent dark matter interpretation for CoGeNT and DAMA/LIBRA

In this paper, we study the recent excess of low-energy events observed by the CoGeNT Collaboration and the annual modulation reported by the DAMA/LIBRA Collaboration, and discuss whether these signals could both be the result of the same elastically scattering dark matter particle. We find that, without channeling but when taking into account uncertainties in the relevant quenching factors, a dark matter candidate with a mass of approximately 7 GeV and a cross section with nucleons of σ DM-N ~ 2 × 10 -4 pb (2 × 10 -40 cm 2 ) could account for both of these observations. We also comment on the events recently observed in the oxygen band of the CRESST experiment and point out that these could potentially be explained by such a particle. Lastly, we compare the region of parameter space favored by DAMA/LIBRA and CoGeNT to the constraints from XENON10, XENON100, and CDMS (Si) and find that these experiments cannot at this time rule out a dark matter interpretation of these signals.

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.

Magnetic trapping of neutrons

Accurate measurement of the lifetime of the neutron (which is unstable to beta decay) is important for understanding the weak nuclear force and the creation of matter during the Big Bang. Previous measurements of the neutron lifetime have mainly been limited by certain systematic errors; however, these could in principle be avoided by performing measurements on neutrons stored in a magnetic trap. Neutral-particle and charged-particle traps are widely used for studying both composite and elementary particles, because they allow long interaction times and isolation of particles from perturbing environments. Here we report the magnetic trapping of neutrons. The trapping region is filled with superfluid 4He, which is used to load neutrons into the trap and as a scintillator to detect their decay. Neutrons in the trap have a lifetime of 750+330-200 seconds, mainly limited by their beta decay rather than trap losses. Our experiment verifies theoretical predictions regarding the loading process and magnetic trapping of neutrons. Further refinement of this method should lead to improved precision in the neutron lifetime measurement.

Dark matter in the coming decade: Complementary paths to discovery and beyond

Dark matter is ve times as prevalent as normal matter in the Universe, but its identity is unknown. Its mere existence implies that our inventory of the basic building blocks of nature is incomplete, and uncertainty about its properties clouds attempts to fully understand how the universe evolved to its present state and how it will evolve in the future. Dark matter is therefore a grand challenge for both fundamental physics and astronomy. At the same time, groundbreaking experiments are set to transform the eld of dark matter in the coming decade. This prospect has drawn many new researchers to the eld, which is now characterized by an extraordinary diversity of approaches unied by the common goal of discovering the identity of dark matter. As we will discuss, a compelling solution to the dark matter problem requires synergistic progress along many lines of inquiry. Our primary conclusion is that the diversity of possible dark matter candidates requires a balanced program based on four pillars: direct detection experiments that look for dark matter interacting in the lab, indirect detection experiments that connect lab signals to dark matter in our own and other galaxies, collider experiments that elucidate the particle properties of dark matter, and astrophysical probes sensitive to non-gravitational interactions of dark matter such as dark matter densities in the centers of galaxies and cooling of stars. In this Report we summarize the many dark matter searches currently being pursued in each of these four approaches. The essential features of broad classes of experiments are described, each with their own strengths and weaknesses. The goal of this Report is not to prioritize individual experiments, but rather to highlight the complementarity of the four general approaches that are required to sustain a vital dark matter research program. Complementarity also exists on many other levels, of course; in particular, complementarity within each approach is also important, but will be addressed by the Snowmass Cosmic Frontier subgroups that focus on each approach. In Sec. II we briey summarize what is known about dark matter and some of the leading particle candidates. In Sec. III, we discuss four broad categories of search strategies and summarize the current status of experiments in each area. We then turn to the complementarity of these approaches in Sec. IV. Conclusions are collected in Sec. V.

Scintillation efficiency and ionization yield of liquid xenon for monoenergetic nuclear recoils down to 4 keV

Liquid xenon (LXe) is an excellent material for experiments designed to detect dark matter in the form of weakly interacting massive particles (WIMPs). A low energy detection threshold is essential for a sensitive WIMP search. The understanding of the relative scintillation efficiency (

Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy β and nuclear recoils in liquid argon with DEAP-1

{\mathcal{L}}_{\mathrm{eff}}

Visualization study of counterflow in superfluid 4He using metastable helium molecules.

) and ionization yield of low energy nuclear recoils in LXe is limited for energies below 10 keV. In this article, we present new measurements that extend the energy down to 4 keV, finding that