November 1999


ORNL researchers savor big role in RHIC’s ‘Big Bang’ experiment

ORNL researchers are contributing to an experiment that scientists hope will simulate the universe moments after the Big Bang. This large-scale endeavor is sited at the newly dedicated Relativistic Heavy Ion Collider facility, which is expected to re-create conditions that could only exist a microsecond after the theoretical beginning-of-everything, or perhaps in the extremely dense centers of neutron stars scattered throughout the cosmos.

A team of researchers from ORNL’s Physics Division, supported by the Instrumentation and Controls Division and the Center for Computational Sciences, is lending the Lab’s expertise in detector and signal processing technology to RHIC’s PHENIX experiment, the largest of a suite of experiments on the new particle collider located at Brookhaven National Laboratory. ORNL is a major contributor to PHENIX, with involvement in constructing and designing the particle detectors and the specialized electronics that will help scientists understand what is detected.

“RHIC is designed to accelerate particles as heavy as gold to almost the speed of light,” says team leader Glenn Young. “Nuclei circulating in opposite directions smash into each other at enormous energies. The goal is to recreate conditions in the center of a neutron star—very hot and very dense—where protons and neutrons melt into quarks.”

“Whether or not quarks separate at all is of interest,” says Physics’ Ken Read. “Because RHIC collides nuclei of the largest available elements containing many protons and neutrons, we’ll get to see a lot of quarks and other particles mingling together, similar to the new state of matter shortly after the Big Bang, except on an infinitely smaller scale. After the Big Bang this state of matter cooled, and certain symmetries evolved.” In other words, the universe came together to form what we know, and are, now.

Physics’ researcher and corporate fellow Frank Plasil says the PHENIX experiment “is a crossroads between nuclear and high-energy physics. We look for photons and other particles and put things together to tell us whether we’ve actually seen this state of matter.” Young comments, “PHENIX is one of RHIC’s detectors that will take a picture, so to speak, of photons and other particles. We’ll get pictures of the initial, and hottest, conditions of the collision.”

The PHENIX experiment is an assemblage of massive steel panels, hair-thin wires and state-of-the-art electronics a world-wide collaboration, that includes ORNL will use to detect particles from a simulated Big Bang.
PHENIX’s look at the collision will be of particular interest because it will provide researchers a record of what happened when it happened, which is important because quarks are in an unnatural state that exists only very briefly—they quickly recombine into nucleonic material (protons and neutrons), as they did after the Big Bang. Other experiments provide information only on the aftermath of such collisions. It is similar, says the team of Lab researchers, to seeing a videotape of an earthquake as it’s happening versus seeing the rubble of the aftermath.

RHIC’s trillion-degrees-hot collisions will result in a spray of up to 20,000 particles as energy is converted to matter, according to Einstein’s famous equation, E=mc2. The PHENIX researchers, however, are only interested in a few. To find them, ORNL researchers and engineers have worked with other institutions to build muon and photon detectors.

Muons are short-lived, elusive particles created in these high-energy collisions that can penetrate many centimeters of steel. The muon detectors are aluminum panels 25 meters square but only a few centimeters thick that are laced with thin-wired tubes that serve as detectors. The detectors are arrayed with steel barriers around RHIC’s collision point. Only the muons can penetrate the steel to strike the detectors, so they can be uniquely identified.

Detecting photons presents a different challenge. Photons, which are electrically neutral, interact in an “all-or-nothing” fashion: They travel in perfectly straight lines without leaving any trace, until they stop completely in dense matter. The PHENIX E-M Calorimeter system detects photons by capturing all of the debris from each photon’s hard collision, acting as the “backstop” behind the rest of the experiment. To ensure good stopping, the calorimeter is made to be as dense as possible—its principal component is lead, in fact, making it one of the heaviest detectors at RHIC.

ORNL’s Physics Division team and their numerous PHENIX collaborators are drawing heavily upon the expertise of the Instrumentation and Controls Division. An I&C group led by Chuck Britton and Bill Bryan has developed application-specific integrated circuits and provided signal processing expertise drawn from years of projects. Most of the PHENIX sub-detectors will rely on ORNL-developed electronics to record accurately the locations and properties of the many particles that strike the sensitive detectors in each RHIC collision and to handle the massive volumes of data that will result.

“You have to sift through many particles as the big nuclei collide,” explains Physics’ Paul Stankus. “There are only one or two from the tens of thousands that we want. There are many individual detectors, and the signals are very small. There is lots of noise. The electronics must be as intelligent and as fast as possible.

“ORNL is on the cutting edge of electronics technologies for physics experiments,” Stankus says.

PHENIX will also draw upon another Lab technology, the High-Performance Storage System, or HPSS, developed at the Center for Computational Sciences, to handle the volumes of data the experiments will generate. RHIC’s detectors produce data by the petabyte, which is a million gigabytes.

How does one store all of that information? ORNL’s solution is the HPSS, which robotically stores, retrieves and loads data similar to a supertech jukebox. “It’s always loading and storing, 24 hours a day. That’s how you keep up,” says Soren Sorensen, a University of Tennessee researcher
ORNL is on the cutting edge of electronics technologies for physics experiments
collaborating with ORNL. “We want a picture, but what we get is many electronic signals. We must change that into actually seeing particles going through our detectors, and you have to teach the computers to see the patterns—connect the dots. Only computers can deal with that much information.”

RHIC’s accelerators began operation in June. The researchers hope to see their first collisions by late winter or early spring. The ORNL/UT PHENIX team, which joins more than 450 members from 45 institutions in 10 countries, includes Young, Read, Plasil, Sorensen, Stankus, Vince Cianciolo, Terry Awes, Yuri Efremenko, post-doc Kyle Pope and graduate student Jason Newby.

The success of another large physics endeavor, the Spallation Neutron Source, hinges on a collaboration of five national laboratories. The PHENIX team notes that such collaborations have long marked high-energy physics experiments as researchers trek to unique facilities to perform their experiments. For the ORNL team, PHENIX is more than an experiment; it is a valuable experience with collaborations that could prove very useful when the SNS is operational.

“RHIC is a beehive; crowded with scientists and users,” says Glenn Young. “That’s how much interest these facilities draw from the research community. You can expect to see that kind of activity and demand at ORNL when the Spallation Neutron Source arrives on the scene.”—B.C. with Vince Cianciolo