Charmonium production in $\bar p$A reactions at threshold
Alexei B. Larionov, Marcus Bleicher, A. Gillitzer, Mark I. Strikman · GSI Repository (German Federal Government) · 2014
Charmonium formation reactions on a proton at rest, pp → R (R = J/Ψ, Ψ , χ c etc.), proceed at the beam momentum p lab = 4 -6 GeV/c.Replacing the proton by a nuclear target one gets a good possibility to explore the interactions of the charmonium with nucleons [1,2].The preference of the antiproton-to other hadron-and photoninduced charmonium production reactions on nuclei is in the slowness of the produced charmonium.Thus, its formation length is small [2].On the other hand, nuclear Fermi motion reduces the cross section strongly, σ pA→R(A-1) * ∼ (10 -4 -10 -3 )Zσ pp→R at the on-shell peak [2], and broadens the beam momentum region by ∼ ±p lab p F /m, where p F 0.3 GeV/c is the Fermi momentum and m = 0.938 GeV is the nucleon mass.The eikonal approximation is well suited to study the pA → R(A -1) * reactions by two reasons: (i) close to the on-shell peak the pp → R formation cross section is large and dominates over other charmonium production channels, and (ii) typical transverse momentum transfers in the formation reaction (∼ p F ) and in the charmonium rescattering processes (∼ 1/ √ B RN 0.6 GeV/c) are much smaller than p lab .Within the Glauber model the charmonium production cross section on a nucleus can be calculated as