Located at Brookhaven National Laboratory, RHIC is a $500M Department of Energy accelerator. When it comes online this year, it will be the first facility in the world capable of producing collisions this energetic. This research will be a major step forward in addressing some exciting questions about subatomic particles: from what happened right after the Big Bang to what gives protons their spin. Dr. Sorensen and Dr. Read of UT's Relativistic Heavy Ion Physics (RHIP) group have had prominent roles in making this work possible.

Dr. Sorensen's route to RHIC began 14 years ago. He was studying the global properties of ultra-relativistic heavy ion collisions at CERN in Geneva and became interested in finding the quark gluon plasma (QGP), a "soup" of the most basic particles within the nucleus, freed from the hadrons that normally hold them together. The QGP is thought to have existed right after the Big Bang and may also be present in the core of neutron stars. Creating and studying this matter can answer basic questions about how the universe began. In 1991, Dr. Sorensen helped draft a proposal to build a detector at RHIC dedicated to this search. Because DOE received a number of proposals for experiments at the Long Island facility, they decided to combine some of the projects.

"Out of the ashes of three proposals came one proposal," aptly named PHENIX, Dr. Sorensen said. PHENIX, one of four experiments at RHIC, is a huge detector system including three electromagnets, four instrumented spectrometers or arms, and two inner detector systems. The scientific group includes more than 400 physicists and engineers. Within this project, Dr. Sorensen has been responsible for the off-line computing system and Dr. Read is responsible for a subdetector called the muon identifier. Dr. Read is also a member of the 12-person PHENIX detector council, a group of subsystem leaders. For now, they're primarily concerned with construction issues. Later, they will be more preoccupied with system operation and upgrades.

"The experiments are so huge, it's either like running a corporation or herding cats," Dr. Read said, pointing out that the project has its own sociology. A high-energy physicist by training, he is accustomed to working with large, expensive experiments involving hundreds of people. He serves as both scientist and manager on the muon identifier, having overcome several hurdles along the way to get the system going.

His first challenge was that circumstances changed and it became apparent that the muon identifier needed to be the first RHIC subdetector completed. However, this part of the project had been deferred at an early stage. So, a tremendous effort became necessary to catch up with the rest of PHENIX and RHIC. Other hindrances outside the team's control included a dropped panel, an accidental flood that engulfed the electronics in a foot of water and mud, and Hurricane Floyd, whose eye just missed the experiment. Nonetheless, Dr. Read's group, including personnel from UT and Oak Ridge National Lab, overcame these obstacles and finished on schedule.

"Oak Ridge-UT met the challenge time and time again in phenomenal ways," Dr. Read said. "It was a race to the finish," but the muon identifier did in fact become "the first active subdetector installed in place at RHIC."

Dr. Read recalls these events with good humor, including the fact that two weeks after he left for a sabbatical at Brookhaven, he found out he was going to be a first-time father. "It all worked out," he said. "We had a beautiful baby and we met the deadline."

Dr. Sorensen's primary task in PHENIX has been developing the off-line computing system-- changing raw electronic signals from the detector into data about the particles for analysis. Test simulations have helped refine the software so that when the experiments begin, the pieces will be in place to speed up publication of the results.

For the scientists involved, simply getting started is the reward for years' worth of work. Both Dr. Sorensen and Dr. Read have been helping set PHENIX in motion since 1991. Dr. Sorensen explained that's a long time to go without the publications or other benefits that usually accompany a well-established research program. For this reason, "RHIC is not a user facility," he said. "One has to have served in the trenches over a substantial amount of time," to participate. Now, however, comes the payoff for all that work.

"Most likely, we will start taking data this spring," Dr. Sorensen said. "This the fun thing--when you get your data and learn something about nature."

While PHENIX is one of four experiments planned for RHIC, all are designed to study the QGP and the nature of fundamental particles.

"The difference between the experiments is how they try to do it," Dr. Sorensen explained. For example, in an airplane crash, the investigation involves putting the various fragments back together and deciding what direction they came from. One experiment (STAR) is looking at as many fragments as possible, whereas the PHENIX group is looking for a few specific pieces. "Only a few out of 10,000 particles will be electrons and muons," Dr. Sorensen said, but they're the pieces that tell you the most about the plasma.

While Dr. Sorensen explores the quark gluon plasma, Dr. Read will be investigating "spin physics." While protons have many properties (mass, charge, …), his group will try to find what gives them intrinsic "spin." By colliding one proton with another proton coming from the opposite direction, they will try to sort out contributions from the complicated constituents spinning around inside a proton (quarks, anti-quarks, gluons, etc.). Dr. Read said unique experimental capabilities will permit fundamental measurements never made before.

"We are poised for world-class data to be coming in," he said." It's guaranteed to pin certain things down one way or the other" and substantially advance the field.

While the RHIC experiments are set to do groundbreaking work in heavy ion collisions, they generated quite a bit of interest this past summer for another reason. Dr. Sorensen explained that because the accelerator has unprecedented power, worries began to surface that it might generate a black hole to swallow the universe, or create bizarre "strange" matter that would wipe out all other matter. Although doomsday stories began popping up in the mainstream press, Dr. Sorensen said scientific journalists took a look at the situation and dismissed the threat. He acknowledges that such rumors go with the territory.

"Every time we have made a new and better, more powerful accelerator" it incites this type of coverage, he said. In the case of RHIC, "we are the first ones to create these collisions artificially," even though the moon is bombarded with a million collisions per second, and, as is easily observed, has not been destroyed by them. "Nature has probed all this for us," he said.

For more information on UT's RHIP group, visit their Web site at http//rhip.phys.utk.edu/rhip. A good overview of RHIC, including information on PHENIX and other experiments, is available at http://www.rhic.bnl.gov.


Back to Cross Sections, Fall 1999 issue.