Narrow Results

The XENON experiment aims at the direct detection of dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off Xe nuclei. The final detector will have a fiducial mass of 1000 kg, distributed in 10 independent liquid xenon time projection chambers (TPCs). Such an experiment will be able to probe the lowest interaction cross-section predicted by SUSY models. The TPCs are operated in dual (liquid/gas) phase, to allow a measurement of nuclear recoils down to < 10 keV energy, via simultaneous detection of the ionization, through secondary scintillation in the gas, and primary scintillation in the liquid. The distinct ratio of primary to secondary scintillation for nuclear recoils from WIMPs (or neutrons), and for electron recoils from background, is used for the event-by-event discrimination. As part of the R&D phase, we built a first XENON module (XENON10) with 15 kg fiducial mass and installed it underground, at the Laboratori Nazionali del Gran Sasso (LNGS), on March 2006. XENON10 has accumulated an exposure of more than 30 live days, operating with quite stable condition. A preliminary analysis of the background data is presented here.

Micropattern detectors (MPD) and in particular MICROMEGAS are being developed very actively in recent years. While increasingly used now in high energy physics experiments, their application to rare event searches is relatively more recent. In this talk the status of three initiatives in this respect are presented: MICROMEGAS for axion searches in the CAST experiment at CERN, the use of MICROMEGAS technology to measure the recoil direction in WIMP searches, and the development of the spherical TPC concept with applications in low energy neutrino detection.

IceCube is a kilometer scale high-energy neutrino observatory, currently under construction at the South Pole. It is a photo-detector, using the deep Antarctic ice as detection medium for the Cherenkov photons induced by relativistic charged particles. These charged particles may be atmospheric muons or reaction products from neutrino interactions in the vicinity of the instrumented volume. The experiment searches for neutrinos originating in astrophysical sources, and can also detect neutrinos from WIMP interaction in the Sun or Earth. In the last two austral summers, 9 in-ice strings and 16 surface IceTop stations (out of up to 80 planned) were successfully deployed, and the detector has been taking data ever since. In this proceedings, IceCube design, present status, performance and dark matter detection sensitivities will be discussed.

We review various issues related to the direct detection of constituents of dark matter, which are assumed to be Weakly Interacting Massive Particles (WIMPs). We specifically consider heavy WIMPs such as: 1) The lightest supersymmetric particle LSP or neutralino. 2) The lightest Kaluza-Klein particles in theories of extra dimensions and 3) other extensions of the standard model. In order to get the event rates one needs information about the structure of the nucleon as well as as the structure of the nucleus and the WIMP velocity distribution. These are also examined Since the expected event rates for detecting the recoiling nucleus are extremely low and the signal does not have a characteristic signature to discriminate against background we consider some additional aspects of the WIMP nucleus interaction, such as the periodic behavior of the rates due to the motion of Earth (modulation effect). Since, unfortunately, this is characterized by a small amplitude we consider other options such as directional experiments, which measure not only the energy of the recoiling nuclei but their direction as well. In these, albeit hard, experiments one can exploit two very characteristic signatures: a)large asymmetries and b) interesting modulation patterns. Furthermore we extended our study to include evaluation of the rates for other than recoil searches such as: i) Transitions to excited states, ii) Detection of recoiling electrons produced during the neutralino-nucleus interaction and iii) Observation of hard X-rays following the de-excitation of the ionized atom.

We consider the hypothesis that dark matter is made of weakly interacting massive particles (WIMPs) and describe how their pair annihilation in the galactic halo generates exotic cosmic ray fluxes. Features for generic WIMP models are reviewed, pointing out cases in which clear signatures arise. Implications from available and upcoming measurements are discussed.

IceCube is a high energy (E ≳ TeV) neutrino telescope currently under construction at the South Pole. The final instrumented volume will be approximately 1 km³ and the complementing surface array (IceTop) will be 1 km² in area. The main objective of IceCube is the search for extraterrestrial sources of high energy neutrinos. IceCube's prototype detector (AMANDA) produced data sets starting in 1997. These have been analyzed in the search for high-energy neutrinos from diffuse and point sources. AMANDA has also performed searches for Dark Matter accumulated in the center of the Earth and the Sun and for relativistic magnetic monopoles. This papers reports the implications of the AMANDA searches and reports on the status of IceCube construction.

We present the current status of the Cryogenic Dark Matter Search (CDMS). The five tower detector array, total 30 detectors, are running stable since October 2006. We have accumulated more than 900 kg-days of low background data. We also summarize the prospect of SuperCDMS project.

Weakly Interactive Massive Particles (WIMPs) are one of the most attractive candidates of Dark Matter in the Universe. The goal of the ArDM collaboration is to develop and operate a liquid argon detector to search for direct evidence of WIMPs. The technical design of the detector aims at independently measuring the scintillation light and the ionization charge generated by the recoil of target argon nuclei after the WIMP collision. A Large Electron Multiplier system will be used to collect the charge while an array of photomultipliers will detect the light. A 1-ton scale prototype is currently under development to demonstrate the feasibility of such a direct detection experiment with large target masses. In this paper, the principle of the experiment and the conceptual design of the detector are described.

Measurement of the direction of the elastic nuclear recoil track and ionization charge distribution along it, gives unique possibility for unambiguous detection of the dark matter WIMP particle. Within current radiation detection technologies only Time Projection Chambers filled with low pressure gas are capable of such measurement. Due to the character of the electronic and nuclear stopping powers of low energy nuclear recoils in the gas, an asymmetric ionization charge distribution along their tracks may be expected. Preliminary study of this effect, called Head-Tail, has been carried out here using the SRIM simulation program for Carbon and Sulfur in 40 Torr carbon disulfide, as relevant to the DRIFT detector. Investigations were focused on ion tracks projected onto the axis of the initial direction of motion in the energy range between 10 and 400 keV. Results indicate the likely existence of an asymmetry influenced by two competing effects: the nature of the stopping power and range straggling. The former tends to result in the Tail being greater than the Head and the latter the reverse. It has been found that for projected tracks the mean position of the ionization charge flows from 'head' to 'tail' with the magnitude depending on the ion type and its energy.

In this talk we present data analysis methods for reconstructing the mass and couplings of Weakly Interacting Massive Particles (WIMPs) by using directly future experimental data (i.e., measured recoil energies) from direct Dark Matter detection. These methods are independent of the model of Galactic halo as well as of WIMPs. The basic ideas of these methods and the feasibility and uncertainties of applying them to direct detection experiments with the next generation detectors will be discussed.

It is now well established that roughly 25% of the total mass-energy density of the Universe is in the form of non-relativistic particles referred to as Dark Matter. This paper will review various ongoing Dark Matter searches and the variety of techniques and implementation used to both detect the rare Dark Matter interactions as well as reject the vast number of background events, with focus given to the recent results obtained in this past year. Eight years into the 21^st century, the field Dark Matter searches is very active, with many new experimental results, and some intriguing hints.

Supersymmetric (SUSY) models with R-parity conservation provide a perfect candidate for Dark Matter searches, The Lightest Supersymmetric Particle or LSP, will be actively searched for with the ATLAS detector at the Large Hadron Collider (LHC). Several SUSY scenarios have been tested and simulation-based results with the first few fb-1 of ATLAS data are presented. Extension of the ATLAS discovery reach to Dark Matter searches show that such measurements can be used to constraint the underlying SUSY LSP scenarios and extract Dark Matter properties.

Questions to discuss:

• What is the origin of the GZK-like suppression of the cosmic ray (CR) flux? Is it due to energy loss during propagation or due to reaching maximum energy achievable in a source?
• Are the data on mass composition of ultra-high energy CRs consistent with a hypothesis that primary particles are 100% proton? Or an admixture of heavy nuclei is also allowed?
• Does the deficit of muons in LHC-tuned MC simulations mean that current hadronic interaction models must be seriously corrected?
• Does the anomalous positron fraction (PF) approach a stable asymptotic value or a sharp cutoff at higher energies is possible?
• Do we observe annihilation of a dark matter or nearby pulsar contribution? Will anisotropy in an arrival direction of CR leptons rule out a dark matter interpretation of PF?
• Is low-mass WIMP region completely excluded by the data?