Cosmology

How do we weigh the Universe? Where is the Dark Matter? I will discuss these questions and show that several independent methods, including the observed present-day abundance of rich clusters , the evolution of cluster abundance with redshift, the baryon-fraction in clusters, the observed Mass-to-Light function from galaxies to superclusters, and other large-scale structure observations, all reveal a universe with a low mass density parameter of ~20% of the critical density. The data suggest that the mass in the Universe, including the dark-matter, approximately follows light on large scales and that most of the mass resides in huge dark halos around galaxies. I will review the combined observational evidence for dark-matter and for dark-energy in the universe and their cosmological implications.

Light hidden sectors are a generic possibility for new physics, and recent astrophysical signals motivate hidden sector dark matter. I will discuss probes of a minimal secluded U(1) hidden sector scenario with high luminosity particle physics experiments.

The XENON project pursues the goal of directly detecting nuclear recoils resulting from scattering interactions with Weakly Interacting Massive Particles (WIMPs), using a phased approach of increasingly more sensitive experiments. The detector consists of a dual-phase liquid/gas xenon time projection chamber, which can measure down to ~2 keV(ee) energy threshold and discriminates against background using both the primary scintillation light and the charge signal resulting from interactions in the noble liquid. The current exeriment XENON100 is the successor of the highly successful XENON10 detector, featuring 10 times greater sensitive mass and 100 times lower background. Its sensitivity with an ultimate exposure of 6000 kg days will be 2 times 10^{-45} cm^2 for spin-independent interactions at 100 GeV/c^2. XENON100 has been installed and is operating. I will report on the present status and discuss its physics reach along with future prospects of detectors at the ton scale.

The DEAP/CLEAN collaboration will be constructing a 3600-kg single-phase liquid-argon dark matter detector at SNOLAB with sensitivity to 10-46 cm2 for a 100 GeV WIMP. We are currently operating a 7-kg liquid-argon detector (DEAP-1) at SNOLAB. Using DEAP-1 we have made measurements of alpha surface activity and radon levels in the detector. We have also performed studies of pulse-shape discrimination to separate electromagnetic interactions in the liquid argon from nuclear recoils. Recently published data from surface at Queen’s University showed no contamination in the WIMP signal region from 16.7 Million tagged gamma events in WIMP the region of interest. A further 22 M events have been accumulated at SNOLAB with no contamination. The design of the DEAP-3600 detector will be presented with emphasis on reduction of backgrounds, including design of a resurfacer to remove radon daughters which plate out on acrylic and the design of the acrylic container to plate shield against neutron activity from the PMTs and steel outer vessel.

Dark sectors with multi-component WIMP states, with small MeV- to GeV-scale splittings, can lead to more complex signatures in direct detection experiments. I'll discuss some scenarios with excited states charged under either the Standard Model or hidden sector gauge groups, and the ensuing constraints.

The ZEPLIN-III liquid xenon dark matter detector has completed its first underground science run, with a final exposure after cuts of 128kg.days of data. This has led to a limit on the spin-independent cross section of 7.8e-8pb for a 60GeV mass WIMP. The required techniques to derive this limit will be outlined, including data stability, detector calibrations, analysis techniques and selection efficiencies. Future plans for ZEPLIN-III will be Outlined. In addition, as a reflection of a new position, the current status of the SNOLab facility will be described, outlining the construction progress, current status of the first experimental suite and future plans and opportunities.