Relativistic Heavy Ion Collider (RHIC) Begins Smashing Atoms

Experiments will yield insights into the structure of matter and how the universe evolved

End view of a gold-ion collision in the STAR detector. enlarge

End view of a gold-ion collision in the STAR detector.

UPTON, NY — Scientists at the U.S. Department of Energy's Brookhaven National Laboratory have begun detecting head-on collisions between gold nuclei in the Relativistic Heavy Ion Collider (RHIC), the world's newest and biggest particle accelerator for studies in nuclear physics. While the beams have been in collision mode since the weekend of June 10, the first spectacular images of particles streaming from a collision point -the definitive evidence the scientists were waiting for - were produced by the STAR detector last night at 9 p.m. High-energy collisions were also seen by the PHOBOS detector early this morning. The collider then began steering beams to the BRAHMS and PHENIX detectors, which will soon begin collecting collision data as well.

"We are crossing into a new frontier of scientific inquiry," said Energy Secretary Bill Richardson. "Scientists from around the world will use this facility to answer some of the most basic questions about the properties of matter and the evolution of our universe."

The collider aims to recreate the conditions of the early universe to gain insights into the fundamental nature of matter - and extend the boundaries of scientific understanding through the 21st century and beyond. Scientists will use data collected during the collisions to explore the particles known as quarks and gluons that make up protons and neutrons. The high temperatures and densities achieved in the collisions should, for a fleeting moment, allow the quarks and gluons to exist "freely" in a soup-like plasma, a state of matter that is believed to have last existed millionths of a second after the Big Bang, when the universe first formed.

Event display of gold-ion collision in PHENIX detector.

Event display of gold-ion collision in PHENIX detector.

Unique facility

"Brookhaven National Laboratory is the only facility in the world where physicists can do this kind of research," said Laboratory Director John Marburger. Previous studies with lower-energy collisions at the CERN laboratory in Switzerland hinted at the existence of quark-gluon plasma. "But RHIC will produce far more definitive results and allow detailed studies of the quark-gluon plasma," Marburger said.

"Detailed studies of the properties of the quark-gluon plasma - such as its temperature, energy and particle densities, and entropy - are essential to really understand and describe this unique form of matter," said Satoshi Ozaki, Associate Laboratory Director for RHIC.

Understanding those properties, in turn, may help explain the origins of protons, neutrons and other elementary particles, and why they form "the dazzling diversity of matter that we see today, including ourselves," said Thomas Kirk, Associate Laboratory Director for High Energy and Nuclear Physics.

"The findings may even have important implications for our understanding of cosmology," added Thomas Ludlam, Deputy Associate Laboratory Director for High Energy and Nuclear Physics, "such as why the universe has its current structure - and where it might be headed."

Two accelerators in one

Event display of particles produced in gold ion-collision as seen by the PHOBOS detector.

Event display of particles produced in gold ion-collision as seen by the PHOBOS detector.

RHIC's unique capabilities stem from its size and dual-ring design. Inside the underground accelerator tunnel are actually two separate accelerator rings, each 2.4 miles in circumference and composed of some 1,740 superconducting magnets. These magnets guide ions of gold atoms - gold nuclei that have been stripped of their electrons - around each of the circular rings in opposite directions at nearly the speed of light. The ions are then stored circulating in the rings at near light speed and allowed to collide at points where the two rings cross.

"The independent acceleration of two separate beams in the collider is what gives RHIC its unique ability to collide heavy ions with such high-energy impact," says Derek Lowenstein, Chairman of Brookhaven's Collider-Accelerator Department.

In this first run, RHIC scientists and engineers achieved collisions with beam energies of about 30 billion electron volts (GeV) per nucleon (proton or neutron) - four times more energetic than the collisions at CERN. Eventually, the Brookhaven scientists will accelerate the ions to collide at energies of 100 GeV per nucleon in each beam - resulting in collisions approximately ten times more energetic than those at CERN.

Particle pressure cooker

With all that energy concentrated in a space about the size of an atomic nucleus, the colliding ions, for a tiny fraction of a second, will reach a temperature one hundred thousand times hotter than the core of the sun - hot enough to "melt" the ions into their component quarks and gluons. By studying the data from millions of these high-energy collisions, RHIC scientists will be able to gather definitive evidence that quark-gluon plasma was formed, and begin to understand its properties.

A collision event recorded by the BRAHMS detector.

A collision event recorded by the BRAHMS detector.

Thousands of particles are emitted following each head-on collision. Sophisticated detectors have been constructed at four of six collision points around the ring to gather and decipher the enormous volumes of data that are recorded regarding the properties of these emitted particles. Two large detectors, PHENIX and STAR, are several stories tall. The other detectors, BRAHMS and PHOBOS, are smaller and more specialized. Scientists will be analyzing data collected by these detectors during continuous runs in the collider throughout the summer. The scientists anticipate releasing the first results from those analyses sometime at the beginning of next year.

Local and international collaboration

RHIC construction began in 1991 and was completed in 1999. Much of the work was done in collaboration with local industry, including the Northrop-Grumman Corporation, which manufactured many of the superconducting magnets at its Bethpage, New York, facility. The experimental program was developed by nearly 1,000 scientific collaborators at nearly 100 research institutions representing 19 countries around the world.

Funded by the United States Department of Energy and constructed by Brookhaven Lab, the RHIC complex builds upon Brookhaven's preexisting chain of accelerators - the Tandem Van de Graaff accelerator, the Booster and the Alternating Gradient Synchrotron. RHIC relies on these other machines to accelerate and inject ions into its collider rings at an energy of about 10 GeV per nucleon.

"This moment represents the culmination of many years of hard work, and now all the pieces are in place," said Satoshi Ozaki. "We have just detected the most spectacular subatomic collisions ever witnessed by humankind, and are launching a new era for the study of nuclear matter."

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