From Brookhaven Lab: “Supercomputing the Transition from Ordinary to Extraordinary Forms of Matter”

Brookhaven Lab

September 18, 2013
Karen McNulty Walsh

Calculations plus experimental data help map nuclear phase diagram, offering insight into transition that mimics formation of visible matter in universe today

To get a better understanding of the subatomic soup that filled the early universe, and how it “froze out” to form the atoms of today’s world, scientists are taking a closer look at the nuclear phase diagram. Like a map that describes how the physical state of water morphs from solid ice to liquid to steam with changes in temperature and pressure, the nuclear phase diagram maps out different phases of the components of atomic nuclei—from the free quarks and gluons that existed at the dawn of time to the clusters of protons and neutrons that make up the cores of atoms today.

But “melting” atoms and their subatomic building blocks is far more difficult than taking an ice cube out of the freezer on a warm day. It requires huge particle accelerators like the Relativistic Heavy Ion Collider, a nuclear physics scientific user facility at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, to smash atomic nuclei together at close to the speed of light, and sophisticated detectors and powerful supercomputers to help physicists make sense of what comes out. By studying the collision debris and comparing those experimental observations with predictions from complex calculations, physicists at Brookhaven are plotting specific points on the nuclear phase diagram to reveal details of this extraordinary transition and other characteristics of matter created at RHIC.

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Nuclear Phase Diagram: This diagram maps out the different phases of nuclear matter physicists expect to exist at a range of high temperatures and densities, but the lines on this map are just a guess. Experiments have detected fluctuations in particle production that hint at where the lines might be; supercomputing calculations are helping to pin down the data points so scientists can make a more accurate map of the transition from the hadrons that make up ordinary atomic nuclei to the quark-gluon plasma of the early universe. The Relativistic Heavy Ion Collider at Brookhaven National Laboratory (RHIC) sits in the “sweet spot” for studying this transition and for detecting a possible critical point (yellow dot) at which the transition changes from continuous to discontinuous. No image credit.

“At RHIC’s top energy, where we know we’ve essentially “melted” the protons and neutrons to produce a plasma of quarks and gluons—similar to what existed some 13.8 billion years ago—protons and antiprotons are produced in nearly equal amounts,” said Frithjof Karsch, a theoretical physicist mapping out this new terrain. “But as you go to lower energies, where a denser quark soup is produced, we expect to see more protons than antiprotons, with the excess number of protons fluctuating from collision to collision.”

By looking at millions of collision events over a wide range of energies—essentially conducting a beam energy scan—RHIC’s detectors can pick up the fluctuations as likely signatures of the transition. But they can’t measure precisely the temperatures or densities at which those fluctuations were produced—the data you need to plot points on the phase diagram map.

“That’s where the supercomputers come in,” says Karsch.

And, this is where we leave it to the professionals. See the full article here.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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