July 22, 2009
Gold Atom Smashups Create New Form of Matter
By Monte Basgall
If you zing a couple of heavy gold atoms around a 2.4-mile underground racetrack at 99.995 percent the speed of light and then let them smash into each other head-on, their crash creates temperatures and pressures greater than those found inside the hottest stars.
The collision's energy is so stupendous that it may actually melt the vacuum of spacetime within a very tiny expanse, summoning up "strange" and "charmed" subatomic quarks that don't frequent today's world, as well as the plain-vanilla quark varieties -- the "up" and the "down."
For less than 0.00000000000000000000001 of a second, these quark swarms are freed from their normally tight bonds with Velcro-like particles of force called gluons. Such liberated "quark-gluon plasmas" assemble very briefly into what scientists are calling a new form of matter within areas only quadrillionths (0.0000000000000001) of a meter wide.
Researchers such as Duke physics faculty members Berndt Mueller and Steffen Bass are tasked with figuring out what actually happens within this space and time span that are too small to measure precisely. They are helping the Brookhaven National Laboratory on Long Island to re-create the first millionths of a second after the Big Bang occurred.
Working with computer clusters at Duke, they are among scores of theoreticians using tools such as histograms -- graph-like assemblages of rectangles -- to visualize what they can't see.
Mueller, a James B. Duke professor of physics who started studying the quark-gluon plasma years before Brookhaven's smashups began, correctly predicted the abundance of extra-heavy strange quarks that are showing up in the national lab's particle detectors. Charmed quarks, ten times heavier than strange ones, are also being produced.
The big surprise is that quarks and gluons don't disassemble into the anticipated hot plasma of electrically charged gas -- the usual definition of "plasma." Instead they form what may be a uniquely free-flowing hot liquid.
Ordinarily, particles with that much energy would be tossing around like ping pong balls, not settling down enough to flow together like water.
"To have a gas-like plasma, the interactions between the particles must be weak," said Mueller. "We found that is not the case. This fluid is very strongly interacting. It has nearly perfect fluidity. The matter that we are seeing is even more interesting than we thought."
The quark and gluon researchers are struck by similarities between this "strongly interacting" hot matter and the strongly interacting cold matter created in the lab of Duke physics professor John Thomas, just one floor down from Mueller and Bass.
Bass, a Duke associate professor of physics, says analyses show the centers of the gold atoms colliding at Brookhaven sometimes create football-shaped, unevenly expanding fluid masses that look and behave much like the ones Thomas has created with ultracold Lithium-6 atoms.
The scientists are now evaluating how the heavy charmed quarks may be interacting with the rest of that quark and gluon medium. Brookhaven experiments suggest the charmed quarks may behave like barreling 18-wheel tractor trailers that are somehow bogged down on a freeway by swarms of tiny motorcycles. "The medium seems to be doing something to them that we haven't 100 percent understood yet," Bass said.
He is working on a "dynamic simulation" with the Renaissance Computing Institute (RENCI), a cooperative venture of the state, the three Triangle universities and five federal agencies that has built a huge touch-activated wall display screen at Duke's Telecom Building, where scientists can create and manipulate complex simulations
“This will permit us to study what’s going on right in the middle of the collision, and how the medium interacts with energetic quarks, both in detail that the measured data alone would never allow,” Mueller said.
The team hopes to learn how charmed quarks lose energy, and how energetic quarks produce a “sonic boom” in the hot liquid.
Monte Basgall is a Senior Science Writer in Duke News and Communications.