UIC scientists recreate the universe’s first moments by slamming together oxygen ions

Barelya fraction of a second afterthe Big Bang, an unimaginably hotand dense mixture of particles, called "quark-gluon plasma,"filled the universe. Fast forward billions of years to today, and physicists can makethis type of matterexperimentally by slamming two atoms together at nearly the speed of light.

"This quark-gluon plasma is the hottest form of matter created by mankind," said Austin Baty, assistant professor of physics at the University of Illinois Chicago. That's 10,000 times hotter than the center of the sun.

Working at the Large Hadron Collider, the world's largest particle accelerator, researchers from the University of Illinois Chicago recently observed the first quark-gluon plasma made with oxygen ions, the lightest particles ever used to make it.

"That was quite exciting for us, because what that means is that quark-gluon plasma is easier to make than we originally thought," said Baty, a leader of the project.

The Large Hadron Collider was built by the European Organization for Nuclear Research, known as CERN, and is used by thousands of researchers from around the globe. Located in Geneva, Switzerland, it pushes particles around a 17-mile ring at super-high speeds. Their collision creates a whole bunch of new particles, which Baty and colleagues then try to "catch" and study with a huge device called the CMS detector. Fifty feet tall and weighing 14,000 tons,the detector is "one of the most complicated experimental apparatuses designed by humans," Baty said.

The collisions recorded by the CMS detector can tell physicists about some of the most fundamental concepts of the universe, like how the parts of an atom stick together. At the center of an atom is its nucleus, an amalgamation of positively charged protons and neutral neutrons, held together by an interaction called the strong force. Though the strong force is foundational to the building blocks of everything on Earth, researchers are still learning how it works.

"The way we can do that is we take the nucleus, and we put it in really extreme scenarios," like slamming two of them together, said Baty. "It turns out if the energy is really, really, really high, you can actually get those protons and neutrons inside of the nucleus to essentially melt," he said. Voila, quark-gluon plasma.

When scientists first set out to make quark-gluon plasma, they took a maximalist approach and used really big nuclei, Baty said. They used ions of lead, which contain a whopping 208 protons and neutrons. Baty and his colleagues wanted to see if they could use nuclei that weren't so heavy. Could they still generate enough energy to melt a nucleus?

The researchers chose oxygen, which only has 16 protons and neutrons. After nearly six months of preparation, the UIC team flew to Geneva and ran the collisions at the Large Hadron Collider in July. They then sorted through the 3 petabytes (or 3,000 terabytes) of data generated from the experiments and ran analyses looking for signatures that confirmed the creation of quark-gluon plasma. The team produced a result in September, a pace Baty described as "ridiculously fast."

"It tells you how hard we were working," he said. "We're really excited, because this result was really pushing the boundaries of what we know about quark-gluon plasma."

The creation of quark-gluon plasma from oxygen collisions will affect how researchers do other experiments at the collider. To study the strong force, it's best to see it in action, Baty said. It's not easy to predict or describe theoretically with calculations on a blackboard, for example.

"The easiest way to study it is just to do experiments and see what actually happens," he said. By showing you can make quark-gluon plasma with oxygen ions, physicists now have another tool in their toolkit to study the strong force.

UIC PhD student Vipul Pant and postdoctoral researchers Sruthy Jyothi Das and Raghunath Pradhan worked closely with Baty on the project. And the thousands of researchers from other institutions who work on the CMS detector were essential partners in the data collection and analysis, Baty said.

"It should not be minimized just how much support we get from the collaboration," hesaid."It's really a huge team effort."