Contrary to what high school students are taught, all matter in the Universe is not composed of tiny atoms. In fact, most matter is composed of something else. Scientists refer to this something else as dark matter.
"Dark matter is the gravitational glue that holds galaxies together," says Richard Schnee, assistant professor of physics in Syracuse University's College of Arts and Sciences. Schnee was recently appointed science coordinator for the Cryogenic Dark Matter Search experiment (CDMS), a collaboration of more than 50 scientists from 16 institutions funded by the U.S. Department of Energy, the National Science Foundation and a number of other public and private organizations. As CDMS science coordinator, Schnee oversees all of the data analysis for the experiment.
"In terms of the total mass of the universe, less than one-quarter of it is made up of the kinds of atoms that make up you and me," Schnee says. "The stars, the earth, everything we see around us is made up of the same atoms, however, most of the mass in the universe is made up of something else. The problem, however, is that dark matter does not emit or reflect light and therefore cannot be observed or detected through conventional means."
Scientific groups across the world are in an international competition to become the first to actually detect dark matter, the building blocks of which may be weakly interacting massive particles (WIMPs). WIMPs travel across space and time through ordinary matter, rarely leaving a trace.
To detect WIMPs, the CDMS group built a series of crystal germanium detectors that are housed in the Soudan Underground Laboratory, north of Duluth, Minn. Theoretical models predict the type of wave patterns that would form if a WIMP hits the nucleus of one of the detector's germanium atoms. Scientists look for those patterns as they analyze the data generated from the detectors.
The CDMS group recently announced that its latest experiments show their detectors are the most sensitive in the world and are poised to "hear" the ring of WIMPs should any of the particles strike. "With our new result we are leapfrogging the competition," says Blas Cabrera of Stanford University, co-spokesperson for the CDMS experiment. "Our experiment is now sensitive enough to hear WIMPs even if they ring the `bells' of our crystal germanium detector only twice a year. So far, we have heard nothing."
While the experiment has not yet detected the elusive WIMPs, Schnee and others are optimistic that it is only a matter of time. "Some well-respected theories of what dark matter is predict that we could have detected it with our experiment," Schnee says. "While we didn't detect any dark matter interactions, it's important to remember that the experiment has not encountered any problems that will limit it in the future. That means the possibility of detecting dark matter in the coming years remains."
Schnee is a member of SU's new multi-messenger cosmology research cluster in the Department of Physics. Multi-messenger cosmology is a field of research that seeks to understand the origin and structure of the universe by observing it through as many "messengers" as possible, including electromagnetic waves (light, radio waves and their cousins), cosmic rays and gravitational waves (waves produced by moving mass, generated from violent events in the universe, which travel at the speed of light). The initiative brings together researchers in the fields of cosmology, astrophysics and particle physics, who study these messenger particles from different perspectives.
Schnee joined the CDMS experiment in 1996 as a visiting scholar at Stanford University, where he oversaw the day-to-day operations of the experiment and co-led the analysis of the first data runs taken from the experiment's original detectors. In 2001, he was appointed analysis coordinator for the project. He arrived at SU last fall after spending seven years at Case Western Reserve University in Cleveland.
