Data from heavy ion collisions give new insight into electromagnetic properties of quark-gluon plasma
UPTON, NY—A new analysis by the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC), a particle collider at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, provides the first direct evidence of the imprint left by what may be the universe’s most powerful magnetic fields on “deconfined” nuclear matter. The evidence comes from measuring the way differently charged particles separate when emerging from collisions of atomic nuclei at this DOE Office of Science user facility.
As described in the journal Physical Review X, the data indicate that powerful magnetic fields generated in off-center collisions induce an electric current in the quarks and gluons set free, or deconfined, from protons and neutrons by the particle smashups. The findings give scientists a new way to study the electrical conductivity of this “quark-gluon plasma” (QGP) to learn more about these fundamental building blocks of atomic nuclei.
“This is the first measurement of how the magnetic field interacts with the quark-gluon plasma (QGP),” said Diyu Shen, a STAR physicist from Fudan University in China and a leader of the new analysis. In fact, measuring the impact of that interaction provides direct evidence that these powerful magnetic fields exist.
More powerful than a neutron star
Scientists have long believed that off-center collisions of heavy atomic nuclei such as gold, also known as heavy ions, would generate powerful magnetic fields. That’s because some of the non-colliding positively charged protons—and neutral neutrons—that make up the nuclei would be set aswirl as the ions sideswipe one another at close to the speed of light.
“Those fast-moving positive charges should generate a very strong magnetic field, predicted to be 1018 gauss,” said Gang Wang, a STAR physicist from the University of California, Los Angeles. For comparison, he noted that neutron stars, the densest objects in the universe, have fields of about 1014 gauss, while refrigerator magnets produce a field of about 100 gauss and our home planet’s protective magnetic field measures a mere 0.5 gauss. “This is probably the strongest magnetic field in our universe.”
But because things happen very quickly in heavy ion collisions, the field doesn’t last long. It dissipates in less than 10-23 seconds—ten millionths of a billionth of a billionth of a second—making it difficult to observe.
So instead of trying to measure the field directly, the STAR scientists looked for evidence of its impact on the particles streaming out of the collisions.
“Specifically, we were looking at the collective motion of charged particles,” Wang said.
Read more on BNL website
Image: Collisions of heavy ions generate an immensely strong electromagnetic field. Scientists investigate traces of this powerful electromagnetic field in the quark-gluon plasma (QGP), a state where quarks and gluons are liberated from the colliding protons and neutrons.
Credit: Tiffany Bowman and Jen Abramowitz/Brookhaven National Laboratory