July 2000

First collisions at RHIC good news for ORNL’s PHENIX collaborators

ORNL researchers were among scientists elated at the first collisions for the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, which occurred on June 12. RHIC’s first collisions were recorded by a succession of detectors.

The 2.4-mile-circumference, dual-ring collider has four detectors—BRAHMS, PHENIX, PHOBOS, and STAR—each built by an international team of researchers to witness and study collisions between gold nuclei traveling close to the speed of light.

“It is, of course, a great achievement—something that we have been looking forward to and working very hard to achieve for a long time,” says Corporate Fellow Frank Plasil of the Physics Division. “After collisions were detected at two other intersection regions, the RHIC people steered the opposing beams of gold nuclei in a way as to also produce collisions in the PHENIX intersection region, where our experiment had no problem in detecting them.”

ORNL’s involvement has been with the PHENIX detector. The detector has benefited from ORNL expertise in detectors and signal processing from the Physics, Instrumentation and Controls and Engineering Physics and Mathematics divisions plus collaborating researchers at the University of Tennessee.

The collisions now under way at RHIC are expected to re-create conditions that could only have existed a microsecond after the Big Bang, or possibly in the extremely dense centers of neutron stars.

Image of an end view of particle tracks streaming from a heavy-ion collision, as recorded by the STAR detector at RHIC.
In those very hot and very dense conditions, protons and neutrons melt into quarks and gluons. Researchers are interested in these states of matter believed to exist shortly after the Big Bang, and how things cooled and condensed to form the universe.

PHENIX offers researchers a real-time record of these collision events, which is important because quarks are in an unnatural state and exist only briefly before recombining into protons and neutrons. Other experiments provide measurements of only the aftermath of the collisions. PHENIX team members say the difference is as marked as seeing a videotape of an earthquake as it is occuring as opposed to seeing only photos of the resulting rubble in the street.

RHIC’s accelerators began operations leading up to the first collisions almost exactly one year ago. The ORNL and UT PHENIX team joins more than 450 members from 45 institutions in 10 countries.

“We are all very excited and full of anticipation to proceed to make physics measurements with the newly available beams,” says Plasil.—B.C.