"Baryon Stopping in Photonuclear Collisions"

Dr. Nicole Lewis, Brookhaven National Laboratory

Photonuclear collisions are one of the simplest processes that can happen in a heavy-ion collision. They occur when one nucleus emits a quasi-real photon which interacts with the other colliding nucleus, similar to an electron-ion collision except that the photon tends to have a much smaller virtuality. Photonuclear collisions can be used to study bulk properties of the medium such as collectivity due to initial-state effects and hadron chemistry. In these photonuclear collisions we observed baryon stopping: more baryons that antibaryons even at angles perpendicular to the beam line. This phenomenon is well documented in proton-proton and heavy-ion collisions, but it is not well understood and had never before been seen in photonuclear collisions. This could indicate the existence of a baryon junction within the nucleon, a nonperturbative Y-shaped configuration of gluons which carries the baryon number and is attached to all three valence quarks. These measurements will also help inform future measurements using particle identification at the upcoming Electron Ion Collider.

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