A New Experiment Recreates Soupy Leftovers of the Big Bang

March 22, 2023

Professor Stefan Bathe leads a team that will study subatomic particles from plasma that existed at the start of the universe.

Group of researches in front of sPHENIX Detector
The sPHENIX detector under construction. The sPHENIX experiment will help scientists learn about quark-gluon plasma (QGP), an exotic form of nuclear matter created in particle collisions at the Relativistic Heavy Ion Collider. (Photo: Brookhaven National Lab, under Creative Commons BY-NC-ND 2.0)

Millionths of a second after the Big Bang, the cosmic explosion that gave birth to the universe, a sea of gluons and quarks formed in a soupy mix today known as quark-gluon plasma. These particles went on to form protons and neutrons, then atoms, and everything we now know that exists in the universe.

Next month, an international team of scientists will unveil a new project designed to recreate the 13-billion-year-old plasma and explore a fundamental force that governs our universe.

The sPHENIX experiment is housed at the Brookhaven National Lab’s Relativistic Heavy Ion Collider (RHIC), one of the largest particle accelerators in the world. As part of a three-year study, physicists will use a 1,000-ton detector to measure particles from collisions of protons and ions traveling close to the speed of light.

The smashups contain the recipe for the particle soup that, physicists say, is very similar to the one that created the ephemeral plasma more than 13 billion years ago.

“Besides the Big Bang, the only way we know how to do it is to accelerate nuclei to very high energies and then collide them,” said Professor Stefan Bathe (GC/Baruch, Physics), a nuclear physicist whose team built part of the detector.   

The Holy Grail of Exotic Nuclear Matter

The collider will smash protons and gold nuclei together in different combinations — gold on gold, proton on proton, and proton on gold. “Gold because it has a very large nucleus, almost 200 nucleons inside,” said Bathe. “This is to make the largest volume of the quark-gluon plasma as possible.”

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For two decades, scientists have known that tiny drops of quark-gluon plasma, or QGP, could be formed by colliding large nuclei, such as gold. But clues emerged that the plasma might be formed by smashups with smaller nuclei. “There were some hints that there might be QGP in smaller systems as early as 2010, but nobody could believe it,” Bathe told the Graduate Center in 2019.

That year, he and other researchers described how they were able to create QGP in collisions of small nuclei in a paper published in Nature Physics.

Those findings came out of the original PHENIX experiment, which Bathe had worked on since 2000. The new project is an extreme makeover of the first, with a new design and upgrades that make it three times as powerful. “It recreates what happened about a millionth of a second after the Big Bang, just on a much smaller scale,” Bathe said.

To generate the magnetic field needed to study the particles, a superconducting magnet at the center of the detector must be cooled to a chilly minus 269 Celsius. In and around the magnet are layers of calorimeters, built to gauge the energy of the particles flying through the plasma.

sPhenix Rendering
A graphic of the sPHENIX detector at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in Upton, Long Island. Illustrated are the detector’s outer and inner hadronic calorimeters, electromagnetic calorimeter, and superconducting solenoid magnet. (Image: Brookhaven National Lab)

Bathe and his team assembled two hadronic calorimeters, which measure streams of hadrons called jets, produced from decaying quarks. “In the collision, thousands of particles fly out in all different directions. And the only way to learn about the quark-gluon plasma is to measure the properties of these particles,” said Bathe.

Four Fundamental Forces of Nature

Like its predecessor, the experiment will shed light on one of the four fundamental forces of nature — the strong force, the weak force, electromagnetism, and gravity.

Bathe’s group — postdoctoral researcher Oliver Suranyi, and Graduate Center Physics Ph.D. students Daniel Richford and Silas Grossberndt — will measure hadrons held together by the strong force. Just how strong is it? According to NASA, the strong force is 100 times stronger than electromagnetism and 100 trillion-trillion-trillion times stronger than puny gravity.

Prof. Stefan Bathe and his group in front of sPhenix detector
Professor Stefan Bathe, postdoctoral researcher Oliver Suranyi, and Graduate Center Physics Ph.D. students Daniel Richford and Silas Grossberndt. The team built two hadronic calorimeters inside the sPHENIX detector at the Relativistic Heavy Ion Collider. (Photo courtesy of Stefan Bathe)

The strong nuclear force binds quarks inside of protons and neutrons found inside the nucleus of atoms, which, in turn, form the basic building blocks of matter. The strong force is carried by gluons and, much like glue, it holds nuclei together. Yet, it remains the least understood of the four forces.

“The quark-gluon plasma is a very complex state of matter with thousands of quarks and gluons inside,” Bathe said, with properties that can’t be predicted on fundamental principles alone.

The physicist pointed to the electromagnetic force for comparison. “All of chemistry, all of biology is fundamentally governed by the electromagnetic interaction,” Bathe said, a force that’s been understood on a fundamental level since the 1940s.

“Nevertheless, there's a rich array of phenomena — think of all of biology, all of chemistry, all condensed matter — that you cannot predict just based on the electromagnetic force. Similarly, quark-gluon plasma is an emergent phenomenon of the strong force. And that's what we're trying to understand.”

Bathe says the sPHENIX experiment will yield its first data set in late September.

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