The University Record, May 8, 1995

New phantom particle could be cold dark matter that holds universe together

By Sally Pobojewski
News and Information Services

Imagine our entire galaxy divided into spaces each about the size of a soccer ball. Inside each soccer ball, picture one invisible particle so tiny it can pass between atoms and zip right through solid objects. No one has ever seen one of these phantom particles. The world's most powerful particle accelerators have no direct evidence that they exist. But, according to physicist Gordon Kane, these ethereal pinpoints in space could be the glue that holds the universe together--the mysterious cold dark matter or "missing mass" which has puzzled cosmologists for the past two decades.

Called LSPs for lightest supersymmetric partner, they are just one of a new class of sub-atomic particles predicted by Kane and a handful of other scientists as part of a new theory in physics called supersymmetry.

Astrophysicists know the total mass our universe must have in order for it to exist in its current form, but stars, galaxies and other types of known matter account for less than 10 percent of this amount. According to the theory of supersymmetry, the combined mass of LSPs scattered throughout the universe produces the remaining 90 percent.

In a presentation at the American Physical Society (APS) meeting held in Washington, D.C.,in April, Kane described recent theoretical developments in supersymmetry, its potential for explaining cold dark matter and its contribution to a new understanding of the fundamental nature of all matter, space and time in the universe. He also described future experiments which could confirm the existence of LSPs.

"Supersymmetry brings us one step closer to answering some of the 'why' questions of our universe," Kane said. "Why does matter exist? What controlled the expansion of the universe after the Big Bang? The world doesn't have to be such a mysterious place. With the addition of supersymmetry, the world becomes a place that makes sense and can be analyzed mathematically."

Supersymmetry is an extension of an established theory in particle physics called the Standard Theory, which describes the structure and organization of matter. According to the Standard Theory, all matter in the universe is made from different combinations of two types of sub-atomic particles. Fermions, such as electrons and quarks, are the "bricks" or fundamental building blocks of matter. A different type of particle called bosons are the "mortar." Bosons are the carriers of forces like electromagnetism and gravity, which hold the "bricks" of our universe together.

"The basic idea of supersymmetry is that every boson has a fermion 'superpartner' and vice versa," Kane said. Most superpartners are heavy with a mass roughly equivalent to the recently discovered top quark. Like the top quark, they exist only for the tiniest fraction of a second before they decay, leaving no physical sign of their existence. This makes them difficult to detect in particle accelerators. "To find them, we have to look for their indirect effects on other particle collision events in the accelerator," Kane explained.

During his APS presentation, Kane described two experiments with the LEP collider at the CERN particle accelerator in Switzerland and explained how apparently inconsistent results in experimental data could be caused by superpartner effects. He also explained how the LSP--the lightest superpartner and the only one that remains stable in nature--could be detected with existing Fermilab particle accelerators upgraded in intensity. Its discovery, Kane said, would be a major step toward confirmation of the theory of supersymmetry.

The research is supported by the U.S. Department of Energy. Others assisting with the research project include postdoctoral fellow Tony Gherghetta, graduate students Chris Kolda and Jim Wells, Steve Mrenna, postdoctoral fellow at Caltech, and Robin Stuart, assistant professor of physics.