Collider is cookin', but is it soup?

An elusive primordial soup of particles may have simmered last year in the Relativistic Heavy Ion Collider, or RHIC, a new particle accelerator at Brookhaven National Laboratory in Upton, N.Y.

The soup would have been a quark-gluon plasma--an astoundingly hot fluid brimming with quarks and gluons, the building blocks of protons and neutrons. In its attempts to make the plasma, RHIC revs gold nuclei to nearly light speed and slams them together (SN:8/26/00, p. 136). The particle collisions have yielded the densest, hottest matter ever observed in a lab.

Last week, physicists presented evidence of RHIC's auspicious debut last summer, when it was powered up to 60 percent of its full energy. They say the machine produced the most promising conditions ever for creating a quark-gluon plasma. For more than a decade, physicists have been trying to study this plasma, which presumably existed just microseconds after the Big Bang, and to observe its transition to ordinary matter.

A year ago, physicists at the European Laboratory for Particle Physics (CERN) in Geneva declared that they had spotted hints of the coveted plasma (SN:2/19/00, p. 117). Now, analyses by RHIC scientists show that show that their collider's subatomic fireballs closely resemble the expected plasma. They presented their results Jan. 15 at the Quark Matter 2001 conference, held at both Brookhaven and the State University of New York at Stony Brook.

In RHIC fireballs, densities soared to at least 20 times that of ordinary nuclei--or at least 50 percent denser than CERN reported, says RHIC physicist John W. Harris of Yale University. Temperatures peaked at an estimated 2 trillion degrees Celsius.

"It's possible that ... we made [the quark-gluon plasma] last summer, but we don't have definitive evidence yet," Harris says. To seek further evidence, scientists plan to crank RHIC up to its full energy this spring.