dr Krzysztof Graczyk

The Nucleon Form Factors

The nucleon form factors have been a subject of intensive theoretical and experimental studies for many years. These functions describe the internal structure of the proton and neutron. The electromagnetic form factors are mainly obtained from elastic electron-nucleon and electron-nucleus scattering data. Q2 dependence of the axial form factor is mainly extracted from quasielastic neutrino-nucleon and neutrino-nucleus scattering data. The strange nucleon form factors, the most unknown, are obtained from parity-violating electron-nucleus as well as from elastic neutrino-matter scattering measurements. The newest electron and neutrino scattering experiments provide us with the higher precision data, and then with electromagnetic and axial form factors, which seem to have different Q2 dependence than the ones obtained from old analyses. In this talk I will focus on the discrepancy between electromagnetic form factors obtained via Rosenbluth separation (e.g. form JLab) and the ones extracted from polarization data (JLab, BLAST, Maintz). It will be shown that Two Photon Exchange correction can explain the problem. For all electromagnetic form factors I will present results of my analyses of the newest experimental data -- the fits of form factors with their uncertainties. The knowledge of the uncertainties plays a crucial role for the extraction of the strangeness of the nucleon (elastic neutrino-nucleon scattering data).