The internal structure of the proton is the result of the strong force, which is by governed Quantum-Chromo-Dynamics (QCD). Experimentally, the internal structure of the proton has been studied extensively through electromagnetic interaction using electron an muon beams. As a result we have precise information about the proton’s charge radius, its electromagnetic elastic and transition form factors, and its quark helicity distribution as represented by the PDFs. While these measurements give us indirect information about effects of the strong interaction in the proton, there is not a one-to-one correspondence between electromagnetic form factors and the strong force acting upon the quarks in the proton. For experiments to be sensitive to the distribution of mass, forces, pressure and angular momentum in the proton, i.e. its mechanical properties, we should employ the gravitational interaction , which is far too weak on our planet to allow any realistic experiments at the subatomic level to be conducted. The discovery and the further development of the framework of generalized parton distribution (GPDs) has opened up this field to the exploration of the strong force in particular exclusive processes, e.g. deeply virtual Compton scattering (DVCS), that mimic the graviton interaction with the proton but at much higher strength making it experimentally accessible.
In this talk I will introduce the underlying background, discuss the experimental methods and the first results of a mechanical property of the proton based on experimental data.
 H. Pagels, Phys. Rev. 144 (1966) 1250-1260
 V. Burkert, L. Elouadrhiri, and F.X. Girod; Nature 557 (2018) no.7705, 396-399
This material is based upon work supported by the US Department of Energy, Office of Science, Office of Nuclear Physics under Contract No DE-AC05-06OR23177