Quarkonium formation time in a model-independent approach

We use dispersion relations to reconstruct, in a model-independent way, the formation dynamics of heavy quarkonium from the experimental data on e⁺e^-→Q̄Q annihilation. We extract a distribution of formation times with a mean value for the J/ψ, 〈τ_J/ψ〉 = 0.44 fm; and for the Υ, 〈τ_Υ〉 = 0.32fm. The corresponding widths of these distributions are given by Δτ_J/ψ= 0.31 fm and Δτ_Υ = 0.28 fm. This information can be used as an input in modeling of heavy quarkonium production on nuclear targets.