182 Progress of Theoretical Physics Supplement No. 149, 2003 Chiral Symmetry Restoration and Anomalous J/ψ Suppression D. Blaschke, 1,2 G. Burau, 1 Yu. L. Kalinovsky 3 and V. L. Yudichev 2 1 Department of Physics, University of Rostock, D-18051 Rostock, Germany 2 Bogoliubov Laboratory for Theoretical Physics, JINR Dubna, Russia 3 Laboratory for Information Technologies, JINR Dubna, Russia (Received May 22, 2003) We investigate the in-medium modification of pseudoscalar and vector mesons within a QCD motivated chiral quark model by solving the Dyson-Schwinger equations for quarks and mesons at finite temperature in the wide mass range from light mesons (π, σρ) to open- charm mesons (D, D * ). At the chiral/deconfinement phase transition, the quark-antiquark bound states enter the continuum of unbound states and become broad resonances (Mott effect). We calculate the in-medium cross section for charmonium breakup processes due to light hadron impact within a chiral Lagrangian approach and show that the Mott effect for the D-mesons effectively reduces the threshold for charmonium breakup and leads to a step-like behaviour of the reaction rate. This is suggested as an explanation of the anomalous J/ψ suppression phenomenon in the NA50 experiment. §1. Introduction The J/ψ meson plays a key role in the experimental search for the quark-gluon plasma (QGP) in ultrarelativistic heavy-ion collisions. The anomalous suppression of its production relative to the Drell-Yan continuum as a function of the centrality of the collision which has been found in 158 AGeV Pb-Pb collisions at the CERN SPS by the NA50 collaboration was suggested before the experiment by Matsui and Satz 1) to be a signal of QGP formation and has therefore been claimed evidence for this new state of matter. 2) Since the first observation of J/ψ suppression in nucleus-nucleus collisions by the NA38 collaboration 3) a debate has been started whether this observation proves QGP formation or whether it can be understood in terms of more conventional hadronic ab- sorption mechanisms on projectile and target nucleons 4) as well as comoving hadrons formed in the collision. 5), 6) So the quest was for both, a refinement and extension of the experimental program as well as for a unifying theoretical approach which would account consistently for the complexity of the processes in high-energy hadronic col- lisions when their description is based on their quark (gluon) substructure including the aspects of the QGP phase transition. In the present contribution we want to elucidate the role which the chiral symme- try restoration transition could play for the explanation of the physical mechanism behind the observed anomalous J/ψ suppression phenomenon. We show that as a result of their quark substructure the hadronic states participating in the J/ψ breakup reactions may undergo a Mott transition when due to the chiral symme- try restoration at high temperatures the quark-antiquark continuum is lowered. In particular, the spectral broadening of D-mesons entails a lowering of the thresh- Downloaded from https://academic.oup.com/ptps/article-abstract/doi/10.1143/PTPS.149.182/1843766 by guest on 01 June 2020