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In this issue:
Faster than a Speeding Bubble
The Search for Dark Matter in the form of WIMPs and the CDMS Experiments
SLAC to Experience Computing Outage
Performance Evaluation Training Sessions
Monday - April 21, 2008 |
Faster than a Speeding BubbleWhat do melting chocolate and bubbles in a champagne glass have in common? Besides being treats one might sample at a sophisticated soiree, they are both handy examples of first-order phase transitions in which a material transforms from one phase to another—that is, atoms changing from an orderly arrangement into a more chaotic arrangement. Now, in an experiment led by Aaron Lindenberg, an international collaboration of scientists has uncovered new clues about the first instants of that process. The results are published in the April 4 edition of Physical Review Letters. "We did not at all expect to see what we saw," said Lindenberg, "although in the aftermath we can go back and realize perhaps we should have. What's amazing about the process is that it spans such a huge range of time scales." The process of melting, or in the case of champagne, of bubbling, has long been of interest to scientists. Phase transitions take place in the tiniest fraction of a second. In the case of Indium Antimonide (InSb), a semiconductor used by scientists to study such processes, the first steps in melting take a few hundred femtoseconds, a quadrillionth of a second. But no one knew what happened after that. Read more... |
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The Search for Dark Matter in the form of WIMPs and the CDMS ExperimentsObservations of galaxies, superclusters, distant supernovae, and the cosmic microwave background radiation, tell us that about 85% of the matter in the universe is not made of ordinary atoms. Deciphering the nature of this dark matter is of central importance for cosmology, astrophysics, and high-energy particle physics. A leading hypothesis is that this dark matter is comprised of Weakly Interacting Massive Particles, (WIMPs), that were produced moments after the Big Bang. If WIMPs are the dark matter, then their presence in our Milky Way may be detectable via scattering from atomic nuclei in a terrestrial detector. The lightest supersymmetric particle (LSP) is an excellent WIMP candidate and is within reach for many models of supersymmetry for both the LHC and direct detection experiments over the next five years, providing a deep complementarity. In this afternoon's colloquium, Stanford's Blas Cabrera will discuss the Cryogenic Dark Matter Search (CDMS) Collaboration, which has pioneered the use of low temperature phonon-mediated detectors to detect the rare scattering of WIMPs on nuclei and distinguish them from backgrounds. Cabrera will describe this powerful technology, which is operating deep underground in the Soudan mine in Minnesota, and compare this approach with new noble liquid techniques that have made recent advances. CDMS II is at the sensitivity frontier for WIMP searches, and its reach is projected to grow by a factor of three by the end of 2008. Cabrera will also describe the new SuperCDMS 25 kilogram experiment, which is partially approved and which will increase sensitivity by an additional factor of 15 by the end of 2012. The colloquium takes place at 4:15 p.m. in Panofsky Auditorium. All are invited to attend. |
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