Understanding the Big Bang: A New Way to Make Particle Soup

Scientists know how to recreate the hot, dense plasma that existed in the early milliseconds of our universe: by accelerating heavy atomic nuclei nearly to the speed of light and smashing them into each other in big particle colliders.

Now, scientists have shown that this early universe particle soup can be created using smaller nuclei than previously thought possible. Professor Stefan Bathe (Baruch College, The Graduate Center, CUNY), graduate students Daniel Richford, Zachary Rowan, and Zhiyan Wang, and former graduate student Jason Bryslawskyj are part of the collaboration of scientists, called PHENIX.

These experiments help physicists learn more about the early moments of our universe and better understand one of the four fundamental forces of nature. The results appear in Nature Physics.

Crashing nuclei into each other breaks down the nuclei’s protons and neutrons into quark and gluon particles. These particles then exist, for a fraction of a second, in a fluid-like state called the quark-gluon plasma (QGP). Small-system collisions can teach scientists about QGP behavior in ways that heavier collisions cannot. This helps researchers learn how matter developed in the milliseconds after the big bang.

Because QGP is governed by the strong interaction, collision experiments also help researchers better understand the theory behind that force. “QGP is one of the phenomena that the fundamental theory predicts,” Bathe said. “We are experimentally trying to see if the predictions of the standard interaction are correct; trying to learn something that theory alone can’t tell us.”

The researchers analyzed flow patterns resulting from smashing gold into a proton, deuteron, and helium-3 nuclei, in a particle collider at Brookhaven National Laboratory, to confirm that the collisions produced QGP.

In the past scientists had only observed QGP in collisions of heavy particles such as gold with gold, so early results of small-system collisions came as a surprise. “Nobody could believe it,” Bathe said, “so we needed to collect a lot of evidence. This paper unambiguously shows that this is QGP.”

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