Mass and Width of J/ψ in QGP from QCD Sum Rule

Behavior of J/ψ in the hot environment is of great interest in high energy heavy ion experiments. Matsui and Satz pointed out that c-cbar cannot form the bound states in quark-gluon plasma created in the heavy ion collisions and this fact would appear as a suppression of the J/ψ yield. Nowadays, J/ψ has been regarded as one of most important probes of the hot matter. Recent theoretical development, however, reveals a quantitave difference from the original argument. Lattice QCD calculation shows that J/ψ survives evenabove T > T_c and melts near T∼ 1.6T_c.
In this work, we investigate possible spectral changes of J/ψ above T_c using QCD sum rule. The QCD sum rule has been shown to givesuccessful description of charmonia in vacuum. It is also applied to analyses of mass in media such as hot hadronic matter and nuclear matter. In this approach, the medium effect can be treated as change of the scalar gluon condensate term and the tensor one in the OPE side of the moment. We determine the temperature dependence of these terms from a lattice QCD data by making use of the fact that these condensates are related to the energy-momentum tensor and thus the equation of state.
For the phenomenological side, we apply the Breit-Wigner form for the imaginary part of the polarization function. We estimate the mass and width of J/ψ at T > T_c by minimizing the squared difference of ratio of the moment between the OPE side and phenomenological side. We find that mass can decrease and the width can be broader even just above T_c.