Physicists working with the ALICE experiment at CERN’s Large Hadron Collider have made the most detailed measurement yet of gluon behavior inside nuclei, finding evidence that the particles may reach a densely packed state known as gluon saturation. “Understanding how gluons behave inside nuclei is therefore essential to understanding how matter itself acquires its mass and structure.” Unlike other measurements that average over the entire nucleus, incoherent J/ψ production is sensitive to local fluctuations in gluon density, allowing the physicists to probe structures smaller than a proton. “Our experiments using incoherent production is like switching from a blurry image to a high-resolution microscope,” Professor Tapia Takaki said. “This process allows us to see how gluons fluctuate and organize themselves inside nuclei.”