by David F. Salisbury

Greene and Maguire

Imagine if you can, a soup of matter and energy so dense that just one teaspoon would weigh 8 trillion pounds.

That is just what an international team of scientists, including several from Vanderbilt, report that they have created with a new atom smasher, called the Relativistic Heavy Ion Collider, at Brookhaven National Laboratory in Long Island, N.Y.

RHIC, which began banging nuclei of gold atoms together head-to-head in June 2000, was designed to recreate the state of matter, called a quark-gluon plasma, that physicists believe exists briefly in the heart of collapsing stars. More importantly, cosmologists think that in the first few millionths of a second following the Big Bang more than 14 billion years ago, the entire universe consisted of this primordial mixture.

Quarks are point-like objects that make up subatomic particles such as protons and neutrons. Gluons are the agents that keep quarks tightly bound within these particles. In normal matter, quarks are never found alone. But theorists predict that a special kind of plasma, in which quarks and gluons roam freely, will form at temperatures about 125,000 hotter than the Sun and at densities dozens of times greater than that of atomic nuclei.

Verifying the existence of such a plasma and determining its physical properties is considered an important key to understanding the events that took place in the early universe. The information may also shed new light on the process of stellar explosions, called supernovae, and the nature of the collapsed objects that they often leave behind.

In its initial runs, RHIC appears to have taken a major step toward the creation of this primitive plasma. The early analysis of the complex spray of particles created in these collisions indicate that it has successfully produced the highest density of matter ever created in an experiment -- a density about 20 times greater than that of the atomic nucleus. Preliminary results of the experiment were announced in mid-January at the Quark Matter 2001 conference held in Stony Brook, N.Y. If confirmed, they will break the previous record set last year by a particle accelerator at CERN, the high-energy physics laboratory located in Geneva.

At the meeting "there was an air of exhilaration and excitement about the results," reported S. Victoria Greene, an associate professor of physics who attended the meeting. She is a member of the team of scientists operating PHENIX, one of two large detectors operating at RHIC. "When the meeting was originally scheduled, the general perception was that RHIC wouldn't be operating long enough to get out any physics. But we had several major new findings."

"The results have far exceeded my expectations," said physics professor Charles F. Maguire, another PHENIX team member. "We've had six months of phenomenally good data!"

According to the two scientists, the initial results suggest that RHIC may already be creating some quark-gluon plasmas, although the accelerator has been operating at an initial power level less than its design maximum. PHENIX measures particles produced in the collisions that fly off perpendicular to the beam line. Greene and Maguire report that some head-on collisions produce fast daughter particles than are produced in more glancing collisions. Although they stress that considerably more work is required before this data is ready for publication, the physicists speculate that this effect could be caused by the formation of quark-gluon plasma. The plasma might work something like molasses to slow the quarks down, causing them to form fewer and slower sub-atomic particles.

In December, Maguire sent an e-mail to colleagues reporting on the experiment's initial success. "It is with great pleasure that I forward to you the news that the PHENIX experiment at RHIC has submitted this week its first ever research publication to the journal Physical Review Letters," he wrote. "First and foremost this publication is the collaborative effort of its 306 authors around the world from 43 institutions. Nonetheless, the fingerprints of the Vanderbilt participants are not difficult to discern."

First, he pointed out that the primary data analyzed in the first paper -- and key data that has been used in most of the initial analyses from PHENIX -- came from a detector subsystem called the Pad Chamber, whose construction was managed by Greene. In fact, many of the Pad Chamber assemblies were built on campus in a special facility on the ninth floor of the physics building.

Maguire, who supervised a team of 40 scientists that developed the software used to analyze the data produced by the detector, developed a software component that played an important role in the data analysis, primarily performed by a group at Weizmann Institute in Israel, that was used in the first paper. In addition, he was one of five team members who wrote the initial draft of the paper, which was then reviewed by all the collaborators.

Meanwhile, Greene was selected to head up the team's internal review committee. The group is charged with double-checking all of the physics results produced by team members to ensure that they are consistent. "We're all susceptible to wishful thinking," said Greene. "We have to be sure that we don't let our desires run away with us."

Finally, Vanderbilt graduate student Kara Adcox will be the first author on the first PHENIX paper. This is the result of the PHENIX policy to list participants alphabetically.

"Kara did significant work in our group for the building of the Pad Chamber assembly," Maguire wrote.

She is one of three graduate students, three post-doctoral associates and a technician who are working with Greene and Maguire on the project. Their participation is funded by the Department of Energy.

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