New LIghts on Dark Matter

Conference Date: 
Thursday, June 11, 2009 (All day) to Saturday, June 13, 2009 (All day)

 

In the last few years, a new observational window has opened on the dark sector of matter. The recent flood of experimental results on direct and indirect dark matter detection has potentially revolutionized our view of the nature of dark matter.

 

As the non gravitational nature of dark matter may well be revealing itself for the first time, initial results have lead to a reexamination of WIMP physics with the aim of enhancing the annihilation cross section through various means, and encouraged theorists to think of more exotic possibilities. The purpose of this workshop is to bring together leading theorists in this area, as well as representatives of the recent experiments, to encourage the sharing and debating of recent results and approaches to probing and describing the dark matter sector.

 

 

Confirmed Invited Speakers To Date

Luca Baldini, INFN-Pias

Pierluigi Belli, DAMA/LIBRA

Marco Cirelli, CEA-Saclay, CNRS

Dan Hooper, Fermilab

Christopher Jillings, DEAP-1

Ann Nelson, University of Washington

Uwe Oberlack, Rice University

Piergiorgio Picozza, PAMELA

Maxim Pospelov, Perimeter Institute & University of Victoria

Wolfgang Rau, CDMS

Adam Ritz, University of Victoria

Pierre Salati, LAPTH

Eun-Suk Seo, ATIC

Alessandro Strumia, Università di Pisa

Tracy Slatyer, Harvard

Nigel Smith, SNOlab

Mani Tripathi, UC Davis/LUX

Liantao Wang, Princeton University

Ubi Wichoski, Laurentian University, PICASSO

Hasan Yuksel, University of Delaware

Jure Zupan, CERN

Kathryn Zurek, Fermilab

 

Luca Baldini, INFN-Pisa

Observation of the high-energy cosmic-ray electron spectrum with Fermi and implications for dark matter scenarios

Successfully launched on June 11, 2008, Fermi is the reference high-energy gamma-ray space observatory of the current decade. The Fermi Large Area Telescope (LAT) has been collecting data continuously in nominal operations since August 2008, providing exciting results that are contributing to changing our understanding of the extreme Universe.

Being a high sensitivity gamma-ray detector, the LAT is by its nature also a powerful electron detector and has in fact delivered the first high precision measurement of the primary cosmic-ray electron spectrum between 20 GeV and 1 TeV, based on six months of data. I will present this result and discuss the implications for dark matter scenarios; possible signatures detectable by Fermi (in both electrons and gammas) that might be helpful to disentangle different models and preliminary results on selected DM searches based on the first 3 months of data will be briefly discussed.


Brian Battell, Perimeter Institute

Hidden sectors at the luminosity frontier

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.,/p>


Pierluigi Belli, DAMA

Signals from the Universe: from DAMA/NaI to DAMA/LIBRA

The highly radiopure about 250 kg NaI(Tl) DAMA/LIBRA set-up is running at the Gran Sasso National Laboratory of the I.N.F.N.. Results exploiting the model independent annual modulation signature for Dark Matter particles in the galactic halo are presented (exposure of 0.53 ton x yr). The DAMA/LIBRA data confirm the evidence for the presence of Dark Matter particles in the galactic halo as observed by the former DAMA/NaI experiment. The combined analysis of the data of the two experiments (total exposure 0.82 ton x yr) gives a C.L. at 8.2 sigma.


Marco Cirelli, CEA-Saclay, CNRS

Seeing Dark Matter in cosmic rays?

Recent data from the PAMELA satellite and a number of balloon experiment have reported unexpected excesses in the measured fluxes of cosmic rays. Are these the first direct evidences for Dark Matter? If yes, which DM models and candidates can explain these anomalies and what do they imply for future searches?


Christopher Jillings, DEAP-1

The DEAP  Dark-Matter Search Program

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.


Ann Nelson, University of Washington,

Slightly nonminimal Hidden sector,Slightly nonthermal relic abundance, and Indirect Detection

I consider a the dark matter relic abundance computation in a model where the dark matter annihilates into a light mediator rather than directly into the standard model. Obtaining the correct relic abundance in such a model may imply a different annihilation cross section than is implied by the usual WIMP decoupling computation. I show that the maximum annihilation cross section is obtained when the hidden sector decouples from the standard model before the dark matter annihilates into the mediator particles, and may be as much as a factor of 5 larger than the standard WIMP value.


Uwe Oberlack, Rice University

Direct Search for Dark Matter with XENON 

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.


Piergiorgio Picozza, PAMELA

Searching for Dark Matter with Cosmic Antiparticles: the PAMELA  Experiment

New results on the antiproton-to-proton and positron-to-all electron ratios over a wide energy range (1 – 100 GeV)  have been  obtained by the PAMELA mission. These data are mainly interpreted in terms of dark matter annihilation or pulsar contribution.  The instrument PAMELA,  in orbit since June 15th, 2006 on board the Russian satellite Resurs DK1, is daily delivering to ground 16 Gigabytes of data. The apparatus is designed to study charged particles in the cosmic radiation, with a particular focus on antiparticles for searching antimatter and signals of dark matter annihilation. A combination of a magnetic spectrometer and different detectors allows antiparticles to be reliably identified from a large background of other charged particles. This talk reviews the design of the apparatus and illustrates the most recent scientific results obtained by PAMELA, together to some of the recent theoretical interpretations. In particular new data on antiprotons, protons, positrons, electrons absolute fluxes will be presented.


Maxim Pospelov, University of Victoria & PI

Superweakly interacting massive particles and their direct detection

KeV-MeV scale dark matter particles with integer spin, very weakly unstable and super-weakly interacting, can produce an observable ionization signal in direct detection experiments. I zoom in on some sensible models and discuss their observational consequences.


Wolfgang Rau, CDMS

Dark Matter Search with CDMS and SuperCDMS

The Cryogenic Dark Matter Search (CDMS) experiment employs cryogenic ionization detectors to search for nuclear recoils induced by Weakly Interacting assive dark matter particles (WIMPs). A fast readout of the thermal energy deposition and the simultaneous measurement of an ionization signal provide an excellent handle for rejection of electron recoil background events from environmental radiation. This unique technology together with passive and active shielding makes CDMS the only background free experiment in the field.

The recently published data based on the full complement of 30 individual detector modules operated in the Soudan Underground Laboratory in Minnesota give the best sensitivity for spin-independent WIMP-nucleon scattering for the most interesting mass range above about 40 GeV/c². The experiment is in a transition to the next phase, SuperCDMS, with increased total target mass and larger individual detector modules with improved sensor technology. SuperCDMS plans to install a total of 100-200 kg of cryogenic germanium detectors in the new SNOLAB facility near Sudbury ON, which, as the deepest large underground laboratory, provides the best conditions for direct dark matter search experiments.


Adam Ritz,  University of Victoria

Novel signatures for direct detection of WIMP dark matter

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.


Pierre Salati, LAPTH

The PAMELA excess int the light of cosmic ray propagation

The positron excess measured by PAMELA may be the long waited hint of the presence of dark matter particles in the Milky Way halo. But before we rejoice, we need to examine the other Possible astrophysical explanations. Whatever the sources -- DM or conventional -- a crucial ingredient is the transport of cosmic rays in the magnetic fields of the Galaxy to which I will pay particular attention in this presentation.


Eun-Suk Seo, ATIC

Recent Results from the ATIC Experiment

The balloon-borne Advanced Thin Ionization Calorimeter (ATIC) experiment has measured the cosmic-ray electron spectrum over the energy range from 20 GeV to 3 TeV.  The totally active Bismuth Germanate (BGO) calorimeter provides energy measurements with resolution of ~2%. The finely segmented Silicon matrix provides charge measurements with an excellent resolution of ~0.2 e.  Below 100 GeV, the ATIC spectrum agrees with previous data and with a calculated spectrum based on a conventional galactic propagation model. Above ~100 GeV the results depart from the calculated spectrum and show an excess electron flux up to about 650 GeV, above which the spectrum drops rapidly. The source of this electron surplus would need to be a previously unidentified and relatively nearby cosmic object within ~1 kilo parsec of the Sun. It could be an astrophysical source, but it might also result from annihilation of dark matter particles. The measurement technique, and the implication of the results will be discussed.


Tracy Slatyer, Harvard

CMB Constraints on Sommerfeld-Enhanced Dark Matter

Dark matter (DM) annihilation around the redshift of last scattering can alter the recombination history of the universe, broaden the last scattering surface, and influence the observed temperature and polarization fluctuations of the cosmic microwave background (CMB). Unlike other indirect astrophysical signals of DM annihilation, these CMB signatures are free of the significant uncertainties inherent in modeling galactic physics, and provide an independent method to test and constrain models of dark matter.  Recently measured anomalous excesses of 10-1000 GeV electron and positron cosmic rays have motivated DM models with large annihilation cross sections when the relative velocity of the annihilating particles is low. We have calculated in detail the efficiency with which energy from DM annihilation is deposited into the photon-baryon plasma around the redshift of last scattering, for an array of annihilation channels, allowing precise predictions of the effect of DM annihilation on the CMB. I will discuss CMB constraints for specific annihilation channels, which can strongly limit the allowed parameter space for DM models fitting the excesses measured by PAMELA and/or Fermi. I will also describe degeneracies between the effect of DM annihilation and changes to the cosmological parameters, and their implications. In particular, DM annihilation could alter the apparent value of the scalar spectral index n_s as measured by WMAP.


Nigel Smith, SNOLab

Latest results form ZEPLIN-III, a liquid xenon dark matter detector, and a status update on SNOLab

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.


Alessandro Strumia, INFN-Pisa

Dark Matter Interpretations of the Electron/Positron Excesses after FERMI

The cosmic-ray excess observed by PAMELA in the positron fraction and by FERMI and HESS in the electron + positron flux can be interpreted in terms of DM annihilations or decays into leptonic final states. Final states into tau's or 4mu give the best fit to the excess. However, in the annihilation scenario, they are incompatible with photon and neutrino constraints, unless DM has a quasi-constant density profile. Final states involving electrons are less constrained but poorly fit the excess, unless hidden sector radiation makes their energy spectrum smoother, allowing a fit to all the data with a combination of leptonic modes. In general, DM lighter than about a TeV cannot fit the excesses, so PAMELA should find a greater positron fraction at higher energies. The DM interpretation can be tested by FERMI gamma observations above 10 GeV: if the electronic excess is everywhere in the DM halo, inverse Compton scattering on ambient light produces a well-predicted gamma excess that FERMI should soon detect.


Mani Tripathi, UC Davis/LUX

The LUX Dark Matter Search Program

LUX (Large Underground Xenon) is a two-phase Time Projection Chamber that will instrument 350 kg of Xenon, 100 kg of which will form a fiducially active target for WIMP interactions.  It will be deployed at the Sanford Underground Science and Engineering Lab at the Homestake Mine in Lead, South Dakota.  The Early Implementation Program of Sanford Lab is providing space at the 4850 feet level for LUX.  The first detector with 120 photomultiplier tubes is being constructed and is projected to start collecting data in late 2009.  Estimated background rates and LUX sensitivity to WIMP like Dark Matter particles will be presented.  At the same time, we are engaged in planning for future detectors of this kind.  Besides scaling to larger target masses, several new technological avenues are also being pursued.  Status of LUX and plans for a roadmap for the future will be presented.


Lian Tao Wang, Princeton University

Capture of Inelastic Dark Matter in the Sun


Ubi Wichoski, Laurentian University, PICASSO

The PICASSO Dark Matter Search Experiment

The PICASSO experiment searches for cold dark matter through the direct detection of weakly interacting massive particles (WIMPs) via their spin-dependent interactions with fluorine at SNOLAB, Sudbury - ON, Canada. The detection principle is based on the superheated droplet technique; the detectors consist of a gel matrix with millions of droplets of superheated fluorocarbon (C4F10) dispersed in it. The previous phase of the experiment, which employed 1-litre detector modules (for a total of about 20g of active mass), ended in 2005. The present phase of the PICASSO experiment consists of 32 4.5-litre detector modules for a total of approximately 1,795 g of active mass. In this talk, I will give an overview of the experiment, discuss the progress in background mitigation, which includes improved purification and fabrication techniques, as well as a background discrimination technique that we have recently discovered. 


Hasan Yuksel, University of Deleware

The origin of the cosmic ray positron/electron excesses in light of the recent observations

The spectra of cosmic ray electrons and positrons should have contributions from known sources such as particles accelerated in supernova remnants and from the cosmic rays interactions.  Besides these guaranteed contributions, any evidence for an additional component may carry hints of a new phenomenon.  Most recently PAMELA and ATIC experiments hinted an overabundance of these particles as compared to model expectations and generated much interest on astrophysical and exotic explanations.  I will first examine the implications of the recent detection of extended, multi-TeV gamma-ray emission from Geminga pulsar wind nebula, which reveals the existence of an ancient/nearby cosmic ray accelerator that can also plausibly account for the observed excess.  Next, I will focus on a possibility that these particles might be produced through dark matter decays/annihilations within the halo of our Galaxy.  I will conclude by reviewing implications of these scenarios for several categories of upcoming Gamma Ray/Neutrino observatories including Fermi and IceCube.