Results from proton-proton bremsstrahlung measurements at 190 MeV

A series of bremsstrahlung measurements have been performed at KVI with the 190 MeV polarized proton beam of the new superconducting cyclotron AGOR. The aim of these measurements is to investigate the dynamics of interactions involving intermediate off-shell nucleons. Nucleon-nucleon bremsstrahlung is the most fundamental process used for such studies as it involves the strong interaction between two nucleons and the well-known electromagnetic interaction. The present experiment provides the most accurate experiment to date on the proton-proton system. The accuracy is high enough to investigate higher order effects such as the virtual Δ-isobar and meson exchange currents. Surprisingly, none of the microscopic calculations is able to describe the data both in magnitude and in shape.