Physicists discover a hidden gluon structure inside protons that could rewrite textbooks

Date: August 16, 2026 Source: Brookhaven National Laboratory Summary: Physicists may have uncovered a hidden feature inside protons that helps preserve one of matter’s most fundamental properties. RHIC collision data suggest baryon number is carried not simply , but by a Y-shaped junction of the gluons connecting them. The finding challenges a decades-old textbook picture and could deepen our understanding of why protons—and ultimately matter itself—remain stable. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY This image shows how, upon impact in a collision (left), a proton's three valence quarks (u, u, d) will continue to fly down the beampipe while the baryon junction, the Y-shaped configuration of gluons, is more easily stopped (right). The baryon junction will pull three new quarks out of the vacuum to become a new baryon, thus retaining the baryon number, while the "freed" quarks will each pair up with a new partner to form mesons. Lentz/Brookhaven National Laboratory New findings from the STAR detector at the Relativistic Heavy Ion Collider (RHIC) are challenging a familiar picture of what gives protons one of their defining quantum properties. The results suggest that gluons, the particles that act as the glue holding quarks together, may play a key role in carrying and conserving baryon number. The evidence comes from high-energy particle collisions at RHIC, a U. Department of Energy (DOE) Office of Science user facility for nuclear physics research that operated at DOE's Brookhaven National Laboratory from 2000 to early 2026. According to the new study, published in Science, baryon number may be associated with a Y-shaped "junction" of gluons connecting the proton's three main quarks. If confirmed, that would challenge the long-standing assumption that baryon number belongs exclusively to those quarks. "Traditionally, scientists have assumed that each of the three main 'valence' quarks inside a proton or neutron carries one-third of the baryon number," said Zhangbu Xu, a professor at Kent State University with a joint appointment at Brookhaven Lab. A Decades-Old Idea About Gluons Physicists first proposed the baryon junction, also called a gluon junction, in the 1970s as a way to describe how gluons connect the valence quarks inside a proton. In 1996, four years before RHIC began operating, Dmitri Kharzeev, a theoretical physicist at Stony Brook University and Brookhaven Lab, proposed that this junction might do something even more fundamental. Rather than the valence quarks carrying baryon number, the junction itself could be responsible. The STAR collaboration has now developed a way to test that possibility using several types of collisions produced at RHIC. "Using data collected from different types of particle collisions at RHIC, our results suggest that the baryon number is not simply carried ," Xu added. "Our findings strongly support the idea that baryon number is more favorably carried and transported by gluons, the particles that hold quarks together, when arranged in this special configuration." Why Baryon Number Matters Determining what actually carries baryon number matters far beyond the internal structure of a proton.