The atomic nucleus, a complex structure comprising protons and neutrons, is held together by smaller particles called quarks and gluons. Despite the initial belief that all the properties of atomic nuclei could be explained using just quarks and gluons, it took decades of relentless research and experimentation to achieve this understanding.
Since protons and neutrons were discovered almost a century ago, scientists have learned they are made of quarks. However, they struggled to reproduce with quark-gluon models the results of nuclear experiments at low energies when only protons and neutrons are visible in atomic nuclei.
Recently, a collaborative effort led by researchers from the Institute of Nuclear Physics in Poland and others has resulted in a significant breakthrough. They found a way to bridge the gap between these two views of atomic nuclei, creating a more comprehensive understanding of their functioning.
Physicists from the IFJ PAN used data from high-energy collisions, like those at the LHC at CERN, to study the partonic structure of atomic nuclei. They focused on Parton distribution functions (PDFs), which show how quarks and gluons are arranged inside protons and neutrons. Understanding these distributions helps scientists predict how particles behave in collisions.
Their innovative work combined traditional nuclear models, which examine the low-energy interactions of protons and neutrons, with PDFs to analyze 18 different atomic nuclei. This new approach allowed them to identify the distributions of quarks and gluons and how nucleons (protons and neutrons) pair up. They found that proton-neutron pairs are the most common, especially in heavy nuclei like gold and lead. This method also improved the accuracy of experimental predictions compared to older techniques.
Dr. Aleksander Kusina, one of the three theoreticians from IFJ PAN participating in the research, said, “In our model, we made improvements to simulate the pairing of certain nucleons. This is because we recognized that this effect could also be relevant at the parton level. Interestingly, this allowed for a conceptual simplification of the theoretical description, enabling us to more precisely study parton distributions for individual atomic nuclei.”
The strong alignment between theoretical predictions and experimental data means that, for the first time, scientists have successfully used the parton model and high-energy data to explain the behavior of atomic nuclei, which was previously understood only through low-energy nucleonic descriptions. This breakthrough offers new insights into the structure of the atomic nucleus, effectively bringing together its high- and low-energy characteristics for a more unified understanding.
Journal Reference:
- A. W. Denniston, T. Jezo, A. Kusina, N. Derakhshanian, P. Duwentaster, O. Hen, C. Keppel, M. Klasen, K. Kovarik, J. G. Morfin, K. F. Muzakka, F. I. Olness, E. Piasetzky, P. Risse, R. Ruiz, I. Schienbein, J. Y. Yu. Evidence for Modified Quark-Gluon Distributions in Nuclei by Correlated Nucleon Pairs. Physical Review Letters. DOI: 10.1103/PhysRevLett.133.152502
