Femto-science: Electromagnetic transition form factors of the nucleon

Project title: Femto-science: Electromagnetic transition form factors of the nucleon
Main applicant: Stefan Leupold, Division of Nuclear Physics
Grant amount: 3 525 000 SEK for the period 2020-2023
Funder: Project grant from the Swedish Research Council

A quantitatively reliable and not only qualitative understanding of the structure of matter at all length scales is one of the fundamental goals of physics research. This application addresses the femtometer scale where the strong interaction shapes the structure of matter. In general, electromagnetic form factors provide insight into the structure of composite objects, because the electromagnetic interaction is so well understood. Already in atomic physics, electromagnetic transitions were instrumental to reveal the intrinsic structure of the atoms. On the experimental side, e.g., JLab in the USA and PANDA+HADES in Germany address baryon transition form factors in different kinematical regimes. Due to the complexity of the strong interaction, mainly phenomenological models have been used in the past on the theory side. Only with recent developments in dispersion theory, chiral perturbation theory and continuum QCD we have now the possibility to progress from a qualitative to a fully quantitative description of baryon transition form factors. This project will harvest the recent theory developments. At present, the transition form factors are particularly not well understood at low energies. This is the regime dominated by pion physics where the model-independent tools of dispersion theory and chiral perturbation theory can be applied, which fits perfectly to the expertise of the applicant. The project aims at an interpretation of JLab data and predictions for PANDA.