Production of J /ψ from nucleus-nucleus reactions depends sensitively on the dissociation cross section with light hadrons. Effective lagrangian methods are used to describe the hadronic degrees of freedom, including strangeness and charm. Cross sections with pions, rho mesons, kaons and nucleons having magnitudes 4-8 mb are found, and with steep thresholds. This, folded with thermal momentum distributions for the scattering partners, suggests a mean dissociation lifetime ≃ 20 fm/c. Therefore, the "abnormal" J /ψ suppression seen in recent Pb+Pb experiments seems to owe to expected hadron kinetics.Response of nuclear matter to high energy densities affords the possibility of creating in the laboratory a system of quantum chromodynamic (QCD) matter, the socalled quark gluon plasma. Among the signatures for creation of the mesoscopic colored volume is an idea put forward in 1986 by Matsui and Satz [1] to look at electromagnetic spectra for evidence of charmonium, bound states of charm-anticharm. They are very tightly bound and consequently relatively small hadrons which ought to effectively probe superdense hadronic matter. Their utility in this context comes from the fact that Debye [color] screening in the plasma would so strongly suppress cc binding in favor of charm propagating decoupled from anticharm to later join with more abundant light anti-quark species forming D mesons, that suppression of J /ψ would indicate plasma formation. Above some critical temperature, the screening radius becomes smaller than the binding radius offering this possibility. J /ψ suppression has since been regarded as a promising signature of quark gluon plasma formation.Charmonium production cross sections from protoninduced reactions that are directly proportional to the target mass number A, are said to be normal. And yet, proton-nucleus and nucleus-nucleus experiments performed over the past several years have exhibited a common A α dependence, with α ≈ 0.92 [2][3][4]. This suppression is now understood as being due to absorption of the precursor state to J /ψ on nucleons and so is in some sense of normal hadronic consequences. Additional sup- *

We calculate the cross sections for reactions of the J/ψ with light mesons. We also evaluate its finite temperature spectral function. We investigate separately the role of elastic and inelastic channels and we compare their respective importance. We describe J/ψ absorption channels that have not been considered previously to our knowledge. The relevance of our study to heavy ion collisions is discussed.

The ω and φ mesons are exceptionally narrow in vacua being about 8 and 4 MeV. At finite temperature they will scatter with other hadrons in their approach to equilibrium and thereafter. These dynamics induce broadening to the already unstable vector mesons which is calculated in the framework of relativistic kinetic theory. A rather complete set of low-lying mesons provide reaction partners whose interactions are modeled using effective Lagrangians. Collision rates for ρ and ω are found to be ∼ 100 MeV at T =200 MeV while the rate for φ is ∼ 25 MeV. Corresponding mean free paths are about 1 and 4 fm! Possible observable consequences are discussed.

Transport models have successfully described many aspects of intermediate energy heavy-ion collision dynamics. As the energies increase in these models to the ultrarelativistic regime, Lorentz covariance and causality are not strictly respected. The standard argument is that such effects are not important to final results; but they have not been seriously considered at high energies. We point out how and why these happen, how serious of a problem they may be and suggest ways of reducing or eliminating the undesirable effects.PACS number(s): 25.75. +r, 24.85. +p