Session H3: Dark Matter

Looking for WIMP Dark Matter using Ultra-Cold Detectors and Other Techniques

Overwhelming observational evidence indicates that most of the matter in the Universe consists of non-baryonic dark matter. One possibility is that the dark matter is Weakly-Interacting Massive Particles (WIMPs) that were produced in the early Universe. These relics could comprise the Milky Way's dark halo and provide evidence for new particle physics, such as Supersymmetry. After briefly reviewing some of the evidence for dark matter and the WIMP hypothesis, I will describe several ongoing searches for dark matter, with an emphasis on those using very low-temperature detectors. In particular, I will present the current results and future plans of our Cryogenic Dark Matter Search experiment, CDMS-II, which aims to see WIMPs using athermal-phonon and ionization sensitive detectors in the Soudan Mine. I will review the status of several other experiments which use a range of methods, from other types of low temperature sensors to promising room-temperature techniques.   

Noble liquid detectors for dark matter.

Experiments based on noble liquid targets are now providing competitive sensitivities in the race for the direct detection of particle dark matter. Theoretical estimates, based on supersymmetric models predict dark matter interaction rates from the best sensitivity of existing direct detection experiments of $\sim $1 evts/kg/month, down to rates of $\sim $1 evts/100 kg/yr, and below this. Current noble liquid experiments for dark matter searches, range in scale from 10 to 1000 kg, and are designed to rise to this challenge. Ar, Ne and Xe targets permit the discrimination of electron recoils, coming from gamma ray and beta backgrounds, versus nuclear recoils, characteristic of WIMP events. This is done using scintillation light pulse shapes, and/or the ratio of ionization to scintillation generated in the target by the interaction. The detectors are also able to significantly reduce backgrounds through the use of position resolution in large volumes, combined with active self-shielding, to reach very low levels in inner fiducial volumes. A growing understanding of how to exploit these characteristics, and construct larger detectors, will allow further significant improvements in the sensitivity of noble liquid experiments. Current and future noble liquid detector experiments include: ArDM, LUX, (mini)CLEAN/DEAP, WARP, XENON, XMASS, XMASS-DM, ZEPLIN   

A microwave cavity search for axions

The mass of the axion, a hypothetical elementary particle proposed as a solution to the ``strong-CP'' problem, is constrained by experimental and astrophysical considerations to a range where the axion is a very plausible cold dark matter candidate. This weakly-interacting dark matter particle could constitute the halo of our galaxy. In the Axion Dark Matter eXperiment (ADMX), halo axions flow through a microwave resonant cavity permeated by a static magnetic field, where some convert into microwave photons. These photons are detected by an ultralow-noise receiver. The ADMX Collaboration has set limits on the axion-to-photon coupling and/or local axion halo mass density for axion mass between 1.9 and 3.3 $\mu$eV. Consideration of phase-space structure of the axion flow, which predicts extremely sharp peaks in the axion kinetic-energy spectrum, improves the limit. Presently underway is an upgrade to the experiment, using SQUID RF amplifiers, which will improve the performance by more than a factor of 10.\\ Work done with L.D. Duffy, P. Sikivie, University of Florida, S.J. Asztalos, G. Carosi, D. Carter, C. Hagmann, D. Kinion, L.J. Rosenberg, K. van Bibber, LLNL, D.B. Yu, MIT, and R.F. Bradley, NRAO.