J/ψ and ψ′ total cross sections and formation times from data for charmonium suppression in pA collisions

The recent data for E866 on the xF dependence for charmonium suppression in pA collisions at 800 GeV are analyzed using a time- and energy-dependent preformed charmonium absorption cross section. For charmonium-nucleon c.m. energy 10 GeV the initially produced premeson has an absorption cross section of σpr≃3 mb. At the same energy but for the developed charmonium states one deduces for the total cross sections σtotJ/ψN=(2.8±0.3) mb, σtotψ′N=(10.5±3.6) mb. The date are compatible with a formation time τ1/2=0.6 fm/c in the rest frame of the charmonium.