J/psi p Scattering Length from GlueX Threshold Measurements

The quality of the recent GlueX J/psi 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/psi-nucleon scattering length \textbar J/psip\textbar is~ provided within the vector meson dominance model. It results in~\textbar J/psp\textbar $=$ (3.08~$+$- 0.55(stat:)~$+$- 0.42(syst:)) mfm which is much smaller~than a typical size of a hadron.