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  • richardmitnick 4:16 pm on February 28, 2014 Permalink | Reply
    Tags: , , , CDMS, , ,   

    From Symmetry: “CDMS result covers new ground in search for dark matter” 

    February 28, 2014
    Kathryn Jepsen

    Scientists looking for dark matter face a serious challenge: No one knows what dark matter particles look like. So their search covers a wide range of possible traits—different masses, different probabilities of interacting with regular matter.

    Photo by Reidar Hahn, Fermilab

    Today, scientists on the Cryogenic Dark Matter Search experiment [CDMS] announced they have shifted the border of this search down to a dark-matter particle mass and rate of interaction that has never been probed.

    “We’re pushing CDMS to as low mass as we can,” says Fermilab physicist Dan Bauer, the project manager for CDMS. “We’re proving the particle detector technology here.”

    Their result, which does not claim any hints of dark matter particles, contradicts a result announced in January by another dark matter experiment [at PNNL], CoGeNT, which uses particle detectors made of germanium, the same material as used by CDMS.

    To search for dark matter, CDMS scientists cool their detectors to very low temperatures in order to detect the very small energies deposited by the collisions of dark matter particles with the germanium. They operate their detectors half of a mile underground in a former iron ore mine in northern Minnesota. The mine provides shielding from cosmic rays that could clutter the detector as it waits for passing dark matter particles.

    Today’s result carves out interesting new dark matter territory for masses below 6 billion electronvolts. The dark matter experiment Large Underground Xenon, or LUX, recently ruled out a wide range of masses and interaction rates above that with the announcement of its first result in October 2013.

    Scientists have expressed an increasing amount of interest of late in the search for low-mass dark matter particles, with CDMS and three other experiments—DAMA, CoGeNT and CRESST—all finding their data compatible with the existence of dark matter particles between 5 billion and 20 billion electronvolts. But such light dark-matter particles are hard to pin down. The lower the mass of the dark-matter particles, the less energy they leave in detectors, and the more likely it is that background noise will drown out any signals.

    Even more confounding is the fact that scientists don’t know whether dark matter particles interact in the same way in detectors built with different materials. In addition to germanium, scientists use argon, xenon, silicon and other materials to search for dark matter in more than a dozen experiments around the world.

    “It’s important to look in as many materials as possible to try to understand whether dark matter interacts in this more complicated way,” says Adam Anderson, a graduate student at MIT who worked on the latest CDMS analysis as part of his thesis. “Some materials might have very weak interactions. If you only picked one, you might miss it.”

    Scientists around the world seem to be taking that advice, building different types of detectors and constantly improving their methods.

    “Progress is extremely fast,” Anderson says. “The sensitivity of these experiments is increasing by an order of magnitude every few years.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

    ScienceSprings is powered by MAINGEAR computers

  • richardmitnick 5:36 pm on September 20, 2013 Permalink | Reply
    Tags: , CDMS, ,   

    From Symmetry: “Scientists expand search for light dark matter” 

    Physicists on the CDMS experiment have devised a better way to search for a particle that, if it exists, would revolutionize our ideas about dark matter.

    side view

    September 20, 2013
    Sarah Witman

    After seeing possible hints of surprisingly light dark matter earlier this year, scientists on the Cryogenic Dark Matter Search have found a way to improve their search for such particles.

    The discovery of low-mass dark-matter particles could tell us that dark matter is more complicated than we originally thought.

    Physicists designed CDMS (pictured above) to look for heavy dark-matter particles, the kind predicted by the popular theory of supersymmetry. Supersymmetry posits that every elementary particle we know—the quark, the lepton, and so on—has a massive partner particle. One such partner particle could be what we call dark matter.

    However, a different theory, currently rising in popularity, predicts the existence of a light dark-matter particle that is just one member in a family of “dark sector” particles.

    “We don’t know; there could be both heavy and light-mass dark-matter particles,” says physicist Dan Bauer, project and operations manager for CDMS and leader of the Fermilab CDMS group. “That’s one of the things that has been interesting in the past few years, the realization that dark matter could be every bit as complicated as normal matter.”

    The CDMS experiment searches for dark-matter particles using a detector filled with germanium and silicon crystals cooled to a very low temperature, about -460 degrees Fahrenheit. Atoms in chilled crystals stay very still, making it easier to notice when they are disturbed. If a dark-matter particle knocks against the nucleus of an atom in the CDMS detector, the interaction will release a small amount of heat and charge, which the scientists measure with sensitive electronics.

    The lighter the particle administering this kick, the smaller the amount of heat and charge released. That makes low-mass dark-matter particles are particularly hard to find.

    A modification to the CDMS detector called CDMSlite—“lite” standing for “low-ionization threshold experiment”—combats this problem with the application of a larger voltage across the crystal (a whopping 69 volts instead of the usual 4). This amplifies the signal that low-mass particles release, giving the scientists a much closer look at the energy range where light dark-matter events should appear.

    The experiment has now set the strongest limits in the world for detection of a dark-matter particle with a mass below 6 billion electronvolts.

    “We are excluding new parameter space that hasn’t been probed before,” says Pacific Northwest National Laboratory physicist Jeter Hall, who conceived of and helped realize the idea of using higher voltages.

    While CDMSlite is not well suited for looking for heavy dark-matter particles—their much-larger signals would saturate the experiment’s electronics—CDMS will not give up on its quest for a massive particle. CDMS scientists will operate detectors in different search modes to cover a wide range of dark-matter masses.

    “We should consider a broad range of possibilities, given how little we know about the properties of dark matter,” says physicist Richard Partridge, who heads SLAC National Accelerator Laboratory’s CDMS group.

    Scientists hope to use the technology developed for CDMSlite in the next generation of the experiment, a larger detector to be placed more than a mile underground at SNOLAB in Canada.

    “The search for dark matter has been on for some time now. Recent evidence points to the possibility of particles lighter than we had anticipated. And hunting for such light dark matter requires newer detection technology,” says Fermilab visiting scholar Ritoban Basu Thakur of the University of Illinois, Urbana-Champaign, who is writing his thesis on CDMSlite. “We are pushing the boundaries of detector technology as we try to find dark matter.”

    CDMS Collaboration

    See the full article here.

    [It seems strange to me that this is the first inkling I have had of this experimentation or its mighty collaboration.]

    Symmetry is a joint Fermilab/SLAC publication.

    ScienceSprings is powered by MAINGEAR computers

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