We use dispersion relations to reconstruct, in a model-independent way, the formation dynamics of heavy quarkonium from the experimental data on e+ e- annihilation to Q-bar Q. We extract a distribution of formation times with a mean value for the J/psi, tau{ J/psi} = 0.44 fm; and for the Upsilon, tau{ Upsilon} = 0.32 fm. The corresponding widths of these distributions are given by Delta-tau{ J/psi} = 0.31 fm and Delta-tau{ Upsilon} = 0.28 fm. This information can be used as an input in modeling of heavy quarkonium production on nuclear targets.
Categories: nucl-th hep-ph