A new publication by the PHENIX Collaboration at the Relativistic Heavy Ion Collider (RHIC) provides definitive evidence that gluon "spins" are aligned in the same direction as the spin of the proton they're in. The result, just published in Physical Review Letters, provides theorists with new input for calculating how much gluons—the gluelike particles that hold quarks together within protons and neutrons—contribute to a proton's spin.
