For the first time in history, quark and gluon tomography of the helium nucleus has been performed. The achievement was made by scientists from the Department of Theoretical Physics at NCBJ. The details are reported in Physical Review Letters.

A paper presenting the first three-dimensional tomography of quarks and gluons in a light atomic nucleus – helium-4 – has been published in the prestigious journal Physical Review Letters. Scientists from the Department of Theoretical Physics (BP2) at the National Centre for Nuclear Research (NCBJ), Dr. hab. Paweł Sznajder and Dr. hab. Jakub Wagner, played a leading role in this research. The latest study demonstrates an innovative application of advanced theoretical methods to provide a precise description of the internal structure of nuclear matter at the subatomic level.

The helium-4 nucleus, also known as an alpha particle, is one of the lightest and most strongly bound nuclear systems. For this reason, it provides an excellent environment for testing and extending tomography methods from individual nucleons (protons and neutrons) to entire atomic nuclei. Understanding how the fundamental building blocks of matter – quarks and the gluons that mediate the interactions between them – are spatially distributed inside the nucleus is one of the major challenges in modern strong-interaction physics. To describe this internal structure, researchers use generalized parton distributions (GPDs), which, among other things, connect information about the longitudinal momentum of quarks and gluons with their spatial distribution (the so-called tomography of hadrons).

To obtain this three-dimensional image, an international research team, including researchers from NCBJ, analyzed a process known as deeply virtual Compton scattering (DVCS). Constructing the theoretical model required highly advanced calculations, including higher-order corrections to the strong interaction and kinematic corrections. This made it possible to observe a clear spatial hierarchy – the resulting tomographic images showed, among other things, that so-called sea quarks and gluons have a significantly broader spatial distribution than valence quarks.

The proposed approach and the theoretical model developed by the researchers provide a foundation for further studies of nuclear GPDs and the experimental measurement programs associated with them. In the near future, new and more precise data for helium-4 will be measured at the U.S. Jefferson Lab (JLab). In the longer term, the methods developed by the researchers will be indispensable for analyzing data from planned electron-ion colliders around the world, such as the EIC in the United States and the EIcC in China.

Detailed research results are available in the following publications:

• Main publication: V. Martínez-Fernández, B. Pire, P. Sznajder and J. Wagner, “Quark and gluon tomography of the helium-4 nucleus”, Phys. Rev. Lett. 137, 111905,
  https://doi.org/10.1103/634s-zcy6 
• Long accompanying article (containing theoretical and methodological details): Phys. Rev. C 114, 035203,
  https://doi.org/10.1103/h7kn-ql7j