The concept of confinement, i.e. the fact that quarks only appear in bound states (hadrons) in nature, has not ceased to puzzle physicists up to now. However, if one goes to high energies the formation of so-called Quark-Gluon-Plasma (QGP) could be possible and the suppressed production of charmonium (J/ψ) in relativistic heavy ion collisions is claimed to be a signature for QGP due to colour screening effects in the plasma. This means that the quarkonia potential range becomes shorter than the size of the resonance making it impossible for the quark and the antiquark to “see” each other and the quarkonium dissociates. More precisely, this phenomenon is probably a complex interplay between suppression of co-mover collisions, colour screening, initial state effects which destroy quarkonia binding processes and the enhancement of charm and anticharm recombination. However, the fact that the magnitude of the J/ψ suppression observed at SPS and RHIC is similar while the centre-of-mass-energy is quite different remains an unsolved mystery. So in order to evaluate and furthermore understand the effect of J/ψ suppression, it is necessary to investigate its dissociation cross section in nuclear matter.

The future experiment PANDA (AntiProton ANnihilations in DArmstadt) at FAIR, which will provide a 1-15 GeV/c antiproton beam, is planned to cover a wide range of QCD-physics topics including reactions –p + A → J/ψ + A-1. J/ψ can be produced at resonance at an incident beam momentum of 4.05 GeV/c following the Breit-Wigner-formula for hadronic resonances. The J/ψ then propagates through the nucleus, with a survival probability proportional to the dissociation cross section, leaves the nucleus and decays. Its leptonic decay channels (J/ψ → e⁺e^–, J/ψ → m⁺m^–) can then be used to detect and reconstruct the event. The respective cross sections are of the order of 100 pb, the total cross section is around 1 b, so a good background suppression of >10¹⁰ is needed. Since the leptonic decay channels are rather “clean”, kinematic and topologic cuts can be applied in order to single out the desired events.

The aim of this work is to implement the theoretical model of the J/ψ interaction with the nuclear environment which was developed by A. Sibirtsev et al. in an event generator for Monte Carlo studies with the simulation and analysis software PandaROOT. The base for the event generator is the software package EvtGen which was developed originally for BaBar and contains decay tables according to the PDG and several decay model routines that can be used independently to model any event of interest.

The data produced with that event generator can then be processed in PandaROOT (which is based on the CERN packages ROOT and GEANT) to simulate events and signals in the detector. UrQMD (Ultrarelativistic Quantum Molecular Dynamics) data will be used to simulate the background.

Furthermore, a detailed study of the actual experimental observables will be done, resulting in a qualitative estimate of the measurability of the J/ψ dissociation cross section with the PANDA experimental setup.

First tests of the EvtGen package and the performance of PandaROOT have been made and an event generator containing the relevant physics is currently in progress.