MSU physicist sheds new light on proton identity in leading scientific journal

Contact: Sarah Nicholas

STARKVILLE, Miss.—What gives a proton its identity? Physicists thought they knew. Now, new experimental findings are challenging scientists’ understanding of what gives these tiny particles their identity—and Mississippi State physicist Wenliang “Bill” Li is helping explain what the results could mean.

Protons are fundamental building blocks of matter and are found in every atom. Understanding how they work gives scientists a window into the forces and particles that govern the physical world.

Li, an assistant professor in MSU’s Department of Physics and Astronomy, has authored an expert perspective “The Proton’s Next Secret,” published in Science, one of the world’s leading scientific journals. His work addresses new results from the STAR Collaboration that provide evidence challenging the traditional understanding of how a proton’s identity is carried within its internal structure. The STAR Collaboration is a global team of more than 600 scientists conducting nuclear physics research with a massive 1,200-ton particle detector at Brookhaven National Lab.

“For decades, we have pictured the proton’s baryon number as being carried by its three valence quarks,” Li said. “These new measurements challenge that simple picture and suggest that the gluon field connecting the quarks may play a much more fundamental role in carrying the proton’s identity.”

At the heart of the research is a property called baryon number, a conserved quantity that helps distinguish matter from antimatter. Protons and neutrons each have a baryon number of one, and understanding where that property comes from inside the proton could reveal new insights into how matter is organized at the most fundamental level.

The new measurements from the STAR Collaboration indicate that baryon number is transported in a way that differs from what would be expected, providing new support for the possibility that the baryon junction plays a key role.

For Li, the new findings offer an opportunity to revisit one of the most basic questions in physics: What, at the most fundamental level, makes a proton a proton?

“If future experiments confirm this interpretation, it would represent an important change in how we think about the proton,” he said.

Li is part of research collaborations at the Thomas Jefferson National Accelerator Facility, commonly known as Jefferson Lab, and the international ePIC Collaboration, both of which investigate the fundamental structure of matter. His work also explores how the questions raised by the STAR results can be tested through electron-scattering experiments at Jefferson Lab and, in the future, at the Electron-Ion Collider.

Li joined MSU’s faculty in 2024 as an assistant professor after holding postdoctoral research positions at the Center for Frontiers in Nuclear Science at Stony Brook University in New York and at William & Mary in Virginia. He earned his master’s and Ph.D. in physics from the University of Regina in Canada in 2017, and a bachelor’s degree in physics from the University of Kent in the United Kingdom in 2010.

For more details about MSU’s College of Arts and Sciences or the Department of Physics and Astronomy, visit www.cas.msstate.edu or www.physics.msstate.edu.  

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