Abstract
The masses of the low lying charmonium states, namely, the J/Ψ, Ψ(3686), and Ψ(3770) are shifted downwards due to the second order Stark effect. In p¯+Au collisions at 6–10 GeV we study their in-medium propagation. The time evolution of the spectral functions of these charmonium states is studied with a Boltzmann–Uehling–Uhlenbeck (BUU) type transport model. We show that their in-medium mass shift can be observed in the dilepton spectrum. Therefore, by observing the dileptonic decay channel of these low lying charmonium states, especially for Ψ(3686), we can gain information about the magnitude of the gluon condensate in nuclear matter. This measurement could be performed at the upcoming PANDA experiment at FAIR.
Highlights
3.0 3.2 3.4 3.6 3.8 M [GeV]responded to the mass shift at the same 0.9ρ0 density
If a meson is generated at a given density, its mass is distributed in accordance with its in - medium spectral function
Results.— In the top panel of Fig. 1 the evolution of the masses of randomly chosen test particles representing charmonium mesons is shown in case of p + Au collisions at 6 GeV bombarding energy
Summary
3.0 3.2 3.4 3.6 3.8 M [GeV]responded to the mass shift at the same 0.9ρ0 density. This gives us a chance to determine the value of the gluon condensate in nuclear matter, at around 0.9ρ0 density, by measuring the distance between the two peaks for Ψ(3686), since we know the dependence of the mass shift of the charmonium on the gluon condensate. The same model was used to study the propagation of low mass vector meson spectral functions at lower energies [20, 29]. In - medium electromagnetic widths are probably larger than the vacuum ones, but to be on the safe side the minimal value is chosen not to overestimate the resulting dilepton invariant mass spectrum in comparison with the background, that is, the genuine change in Γeρl could only increase the spectrum not decrease.
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