March 15, 2010
Jeremy Craig, 404-413-1357
Scientists believe that, for a few microseconds at the beginning of the universe, a type of extremely high temperature plasma "soup" would cool to become the basis for all matter.
To help explain this theory surrounding this soup - called quark-gluon plasma - scientists at the Brookhaven National Laboratory in Upton, N.Y., used a huge particle accelerator to collide gold particles traveling at nearly the speed of light. In doing so, they created the hottest temperature ever recorded in a laboratory - about 250,000 times hotter than the center of the sun.
Georgia State University physicists played a role in this discovery, helping to calculate the temperature of the collision - 7.2 trillion degrees Fahrenheit (4 trillion degrees Celsius).
The collision at the U.S. Department of Energy's Relativistic Heavy Ion Collider (RHIC) ultimately offers insight into the fundamental structure of matter, and of the early universe. The findings will be published in Physical Review Letters.
"At the lab, we collide the nuclei of gold atoms to compress them to the densest form possible. And when the collision occurs, a lot of energy is dumped in a very small region," said Xiaochun He, head of the GSU Nuclear Physics Group (NPG) and professor of physics.
Temperatures can be indicated by color. For example, iron glows orange or red when heated, but as heat gets higher, the color becomes bluish. But at the subatomic level, detecting light can be difficult to do. To calculate the temperatures, He said that scientists measure distributions of very energetic light particles, or photons, radiating from the collisions.
The temperature calculation is based upon measurements by the Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) Collaboration, of which GSU's Nuclear Physics Group has been a part of since the mid-1990s.
The PHENIX Collaboration's primary goal is to discover and study quark-gluon plasma. The temperature reached in the recent experiment at the RHIC is higher than the temperature needed to melt protons and neutrons - elements of the nuclei of atoms in all matter - into this plasma. Such plasma is believed to have filled the universe for a few microseconds after the Big Bang.
"We still have a lot of work to do," He said. "We're trying to look at the system and ask, 'if the system has such a high temperature, how have other particles produced or evolved when the system cools or expands?'"
Scientists continue to collide gold nuclei, and members of GSU's NPG spent spring break taking shifts to collect more gold collision data for further data analysis. Two current Ph.D. students in the group are going to use this data set for their dissertation projects.
Georgia State's NPG has made several contributions to PHENIX. On the physics data analysis front, two other Ph.D. and two master's students at GSU have completed their research studied with the PHENIX experiment data. Their studies will further help scientists to characterize the properties of matter at such high temperature and densities, which are created from gold on gold collisions.
From 1994 to 1996, the NPG group worked on simulations for optimizing detector components which identify a type of particle called muons, in order to separate these particles from other particles created in nuclear collisions. From 1997 to 2004, the NPG group focused on a component of the PHENIX Online Data Acquisition system.
This group is also working on an upgrade for the PHENIX detector system which will allow for measurements that will show light on the mysteries of the proton spin, helping scientists to understand the composition of protons. This is the research focus of assistant professor Murad Sarsour, who joined the Department of Physics and Astronomy during the fall of 2008.
For more about physics at Georgia State, visit www.phy-astr.gsu.edu. A visual simulation of the collision is available from the Brookhaven National Laboratory at www.youtube.com/watch?v=kXy5EvYu3fw. For more about the PHENIX experiment, visit www.phenix.bnl.gov.