Influence of elementary particles on the structure of atomic nuclei

Researchers analyse binding of nucleons in atomic nuclei at the quark-gluon level for the first time / Bridge from nuclear to particle physics

In particle physics, quarks are known as the building blocks of nucleons - protons and neutrons - as well as their binding through the strong nuclear force mediated by gluons. How this force also indirectly holds nucleons together in atomic nuclei, however, is one of the most important current questions in nuclear physics. The fact that the bound states of two nucleons play a special role in atomic nuclei is already known from nuclear physics experiments at low energy. Now, a team from Europe and the USA led by Dr Tomáš Ježo and Prof Michael Klasen from the Institute of Theoretical Physics at the University of Münster has investigated these bound states at a higher resolution for the first time. To do this, they analysed particle physics data obtained at very high energies, for example at the LHC particle accelerator at CERN in Geneva. These experiments are comparable to a microscopic examination. The higher the energy, the greater the resolution with which the nuclear building blocks can be analysed.

"To our surprise, despite the very different approaches, we found the same abundance of nucleon pairs as our colleagues had previously found at low energies," says Tomáš Ježo. "Furthermore, we were able to show for the first time that quarks and gluons behave differently in these pairs than in free nucleons and also differently than previously expected in atomic nuclei. This has a decisive influence on our understanding of nuclear binding." The study also shows that the abundance of pairs increases with nuclear mass and that proton-neutron pairs are particularly common.

For the study, the research team extended the "parton model of quantum chromodynamics", which mathematically describes the interactions in atomic nuclei, by integrating individual nucleons and pairs of correlated nucleons into the analyses for the first time. The results have been published in the journal Physical Review Letters.