Direct photons offer glimpse of gluons’ dynamic motion

Scientists seeking to explore the teeming microcosm of quarks and gluons inside protons and neutrons report new data delivered by particles of light. The light particles, or photons, come directly from interactions of a quark in one proton colliding with a gluon in another at the Relativistic Heavy Ion Collider (RHIC). By tracking these ‘direct photons,’ scientists say they are getting a glimpse — albeit a blurry one — of gluons’ transverse motion within the building blocks of atomic nuclei.