Status of the CDMS search for WIMPs

The Cryogenic Dark Matter Search (CDMS) experiment uses germanium and silicon detectors cooled to 20 mK to attempt to detect weakly interacting dark matter particles in our galactic halo. We discuss recent results obtained with an array of two 165 g germanium detectors and a 100 g silicon detector after a 33 live-day exposure. I THE CHALLENGE OF WIMP DETECTION. One possible solution to the famous \dark matter problem" is that the dark matter is in the form of weakly interacting massive particles (WIMPs), which could be, for example, the neutralinos predicted by supersymmetry [1]. These particles should have masses in the range 10 10 GeV. Large numbers of them could have been produced in thermal equilibrium in the early Universe. Today, they would be present in the dark halo of the Galaxy, which is known to have a local density of ' 0:4 Gev/cm. If the halo mass is dominated by WIMPs of mass m, they should have a local ux of (m=1 GeV ) 10cm s 1 and might be detected via interactions with detectors on Earth. Unfortunately, the small interaction cross sections on atomic nucleii imply very low event rates (< 0.01 event/kg-day) and the energy transferred to the nucleus is also low ( 10 keV). 1) The CDMS collaboration: D.S. Akerib, P.D. Barnes Jr., D.A. Bauer, A. Bolozdynya, P.L. Brink, B. Cabrera, D.O. Caldwell, J.P. Castle, R.M. Clarke, P. Colling, M.B. Crisler , A. DaSilva, A.K. Davies, R. Dixon , S. Eichblatt ,, R.J. Gaitskell, S.R. Golwala, E.E. Haller, J. Hellmig , M.E. Huber, K.D. Irwin , J. Jochum, F. Lipschultz, J. Martinis , S.W. Nam, B. Neuhauser, H. Nelson, T.A. Perera, R.R. Ross, T. Saab, B. Sadoulet, R.W. Schnee, T. Shutt, A. Smith, A. Sonnenschein, A.L. Spadafora, W.K. Stockwell, S. Yellin, B.A. Young Case Western Reserve University, Cleveland, OH. Lawrence Livermore National Laboratory, Livermore, CA. University of California, Santa Barbara, CA. Stanford University, Stanford, CA. San Francisco State University, San Francisco, CA. Fermi National Accelerator Laboratory, Batavia,IL. Center for Particle Astrophysics and Department of Physics, University of California, Berkeley, CA. Lawrence Berkeley National Laboratory, Berkeley, CA . University of Colorado, Denver, CO. National Institute of Standards and Technology, Boulder,CO. Princeton University, Princeton, NJ. Santa Clara University,Santa Clara, CA. Address inquiries to [email protected]. FIGURE 1. Demonstration of nuclear recoil discrimination in a 165 g thermistor-instrumented Ge detector. The ratio of the ionization and thermal signals is plotted as a function of recoil energy for exposure to a Co-60 gamma ray source (left) and a Cf-252 neutron source (right). 0 20 40 60 80 100 0 0.5 1 1.5 Recoil Energy [keV] C ha rg e E ne rg y/ R ec oi l E ne rg y [k eV /k eV ]