Recent experimental data and the size of the quark in the Constituent   Quark Model
  We use the Constituent Quark Model (CQM) to describe CDF data on double parton cross section and HERA data on the $ J / \Psi$ ratio cross section of elastic and inelastic diffractive productions. Our estimate shows that the radius of the constituent quark turns out to be rather small, $R^2_{quark} \approx 0.1 Gev^{-2}$, in accordance with the assumption on which CQM is based. 
S.Bondarenko, E.Levin, J.Nuiri