New CERN measurement challenges conventional models of how gluons behave inside atomic nuclei

A groundbreaking measurement conducted by physicists at CERN’s Large Hadron Collider has cast doubt on long-standing assumptions about how gluons behave within atomic nuclei. The findings, led by a researcher from the University of Kansas and published in Physical Review Letters, mark a pivotal moment in nuclear physics, offering the first multidimensional analysis of incoherent J/ψ photonuclear production. This method enables scientists to examine the distribution of gluons, the particles responsible for binding quarks, with unprecedented precision. The experiment took place within the ALICE detector at CERN, utilizing data gathered during the second run of the Large Hadron Collider. During this period, fast-moving lead nuclei passed near each other without direct collisions, generating intense electromagnetic fields that behaved like beams of high-energy photons. When these photons interacted with other nuclei, they produced J/ψ mesons, which serve as a sensitive indicator of the internal gluon structure. Unlike previous methods that averaged results across the entire nucleus, this technique allowed researchers to detect variations in gluon density at subatomic scales. Daniel Tapia Takaki, a nuclear physicist at the University of Kansas and a key figure in the study, explained that the measurement revealed how gluons fluctuate and organize within nuclei. By adjusting the momentum transfer, the team effectively altered the “resolution” of their observations, probing increasingly smaller regions within the nucleus. At the highest resolution, approximately 0.2 femtometers, the experiment captured structures roughly a quarter the size of a proton. If a nucleus were the size of a football stadium, this level of detail would allow researchers to discern features just a few yards across. Tapaki emphasized that these findings suggest gluons begin to exhibit collective behavior at such small scales, a phenomenon referred to as gluon saturation. This observation challenges existing theories that describe gluon interactions as independent rather than coordinated. The results have implications beyond nuclear physics, potentially influencing our understanding of how matter gains mass through the strong force. The study builds upon earlier work by Takaki, who has pioneered techniques to analyze localized regions of high gluon density, sometimes termed “hot spots.” His theoretical models predicted that these dense areas could evolve with increasing collision energy and might reveal novel aspects of the strong interaction. The current research extends this framework by measuring incoherent J/ψ production across a broad spectrum of photon-nucleus energies, providing empirical support for these hypotheses. Collaboration between the University of Kansas and the Czech Technical University in Prague played a crucial role in the project. The partnership facilitates ongoing exchange of researchers and resources, contributing to the success of the experiment. Takaki noted that the ability to distinguish between competing models of gluon behavior represents a major step forward in unraveling the complex dynamics of nuclear matter. As the scientific community continues to refine its understanding of the fundamental forces governing the universe, this discovery underscores the importance of advanced experimental techniques in probing the inner workings of matter. Future studies will likely build on these insights, further exploring the intricate interplay between gluons and the properties of atomic nuclei.