We study hadron properties near the deconfining transition in the finite temperature lattice QCD. This paper focus on the heavy quarkonium states, such as $J/psi$ meson. We compare the meson correlators above and below $T_c$ and discuss the possibility of the $cbar{c}$ bound state by observing the wave function.
Dissociation temperatures of J/psi, psi, and chi_c states play key roles in the sequential J/psi suppression scenario for high energy heavy ion collisions. We report on a study of charmonium dissociation temperatures in quenched lattice QCD. On anisotropic lattices, we first subtract the effects of the constant mode in finite temperature meson correlators, which have lead to unphysical results in previous studies. We then extract ground and first exited state masses by diagonalizing correlation functions among different source and sink operators. To distinguish bound states from scattering states, we first compare the charmonium mass spectra under different spatial boundary conditions, and examine the shape and the volume-dependence of their Bethe-Salpeter wave functions. From these studies, we found so far no sign of scattering states up to about 2.3T_c.
I review a selection of recent finite temperature lattice results of the past years. First I discuss the extension of the equation of state towards high temperatures and fi- nite densities, then I show recent results on the QCD topological susceptibility at high temperatures and highlight its relevance for dark matter search.
Working with a large basis of covariant derivative-based meson interpolating fields we demonstrate the feasibility of reliably extracting multiple excited states using a variational method. The study is performed on quenched anisotropic lattices with clover quarks at the charm mass. We demonstrate how a knowledge of the continuum limit of a lattice interpolating field can give additional spin-assignment information, even at a single lattice spacing, via the overlap factors of interpolating field and state. Excited state masses are systematically high with respect to quark potential model predictions and, where they exist, experimental states. We conclude that this is most likely a result of the quenched approximation.
In the last couple of years, there has been big progress in finite temperature QCD on the lattice. Large-scale dynamical simulations of 2+1 flavor QCD with various improved staggered quark actions have been started to produce results for various thermodynamic quantities which are extrapolated to the continuum limit at around physical quark masses, and thus are capable for a direct comparison with experiment. At the same time, the theoretical uneasiness with staggered-type lattice quarks motivated several groups to accelerate studies with Wilson-type quarks and lattice chiral quarks. In this review, I discuss these important developments in finite temperature QCD made in the past year.
We compute charmonium spectral functions in 2-flavor QCD on anisotropic lattices using the maximum entropy method. Our results suggest that the S-waves (J/psi and eta_c) survive up to temperatures close to 2Tc, while the P-waves (chi_c0 and chi_c1) melt away below 1.2Tc.