LHC Ultraperipheral Collisions Unravel the Mystery of Gluon Saturation
Ultraperipheral collisions (UPCs) at the Large Hadron Collider (LHC) offer a unique window into gluon dynamics. Experiments use photons to probe gluons within protons and nuclei, investigating gluon saturation—a dynamic equilibrium between gluon splitting and recombination. Researchers found that as energy decreases, the number of gluons in hadrons increases, forming 'gluonic hotspots' that overlap in the gluon saturation regime. The experiments also observed nuclear shadowing, where nuclei contain fewer gluons than expected. These findings shed light on the origin of 99% of the visible universe's mass and the nature of the strong interaction. Future LHC runs and the Electron-Ion Collider (EIC) will further explore gluon dynamics, uncovering more mysteries.