J / ψ p scattering length from GlueX threshold measurements

The quality of the recent GlueX J/ψ photoproduction data from Hall D at Jefferson Laboratory and the proximity of the data to the energy threshold, gives access to a variety of interesting physics aspects. As an example, an estimation of the J/ψ-nucleon scattering length αJ/ψp is provided within the vector meson dominance model. It results in |αJ/ψp| = (3.08 ± 0.55 (stat.) ± 0.42 (syst.)) mfm which is much smaller than a typical size of a hadron.