A study of charmonium systems across the deconfinement transition

We present results from lattice studies of charmonium systems near the deconfinement transition temperature. On quenched isotropic lattices with lattice spacings between 0.02 and 0.05 fm, qq systems with quark masses close to the charm mass and with different spin-parity quantum numbers are studied in the temperature range 0.9T_c-3T_c. Results for temporal correlators of local operators, and the spectral functions constructed from them, are discussed. For the pseudoscalar and vector channels, the correlators are observed to change very little across the deconfinement transition, unlike in the case of the light quarks. (orig.)Available from TIB Hannover: RA 2999(02-108) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Temporal propagators and quasiparticles in hot QCD

We have calculated the temporal quark and gluon propagators on large (64"3 x 16) isotropic lattice and extracted the spectral function from them. Calculating the spectral function at several spatial momenta we were able to determine the dispersion relation for quarks and gluons and extract the temperature dependent quasiparticle masses. We have found that the quasiparticle masses measured in units of temperature increase substantially as the temperature is lowered from 3T_c to 1.5T_c. Our temporal propagators are quite different from those calculated within the HTL perturbation theory. We have found that in general medium effects are stronger than suggested by hard thermal loop perturbation theory. In particular, the quasiparticle masses determined by us are generally larger than those predicted by HTL perturbation theory (except for the gluon mass at 3T_c). We also see a large continuum contribution in the gluon spectral function which is absent in the HTL approximation. (orig.)Available from TIB Hannover: RA 2999(02-109) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

A lattice calculation of thermal dilepton rates

Using clover improved Wilson fermions we calculate thermal vector meson correlation functions above the deconfinement phase transition of quenched QCD. At temperatures 1.5 T_c and 3 T_c they are found to differ by less than 15% from that of a freely propagating quark anti-quark pair. This puts severe constraints on the dilepton production rate and in particular rules out a strong divergence of the dilepton rate at low energies. The vector spectral function, which has been reconstructed using the Maximum Entropy Method, yields an enhancement of the dilepton rate over the Born rate of at most a factor two in the energy interval 4<or#approx##omega#/T<or#approx#8 and suggest that the spectrum is cut-off at low energies by a thermal mass threshold of about (2 - 3) T. (orig.)Available from TIB Hannover: RA 2999(01-175) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Hadron correlators, spectral functions and thermal dilepton rates from lattice QCD

We discuss information on thermal modifications of hadron properties which can be extracted from the structure of Euclidean correlation functions of hadronic currents as well as more direct information obtained through the reconstruction of the spectral functions based on the Maximum Entropy Method. (orig.)Available from TIB Hannover: RA 2999(02-153) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Behavior of charmonium systems after deconfinement

We present a study of charmonia in hot gluonic plasma, for temperatures upto three times the deconfinement transition temperature T_c. qq systems with quark masses close to the charm mass and different spin-parity quantum numbers were studied on very fine isotropic lattices. The analysis of temporal correlators, and spectral functions constructed from them, shows that the J/#psi# and #eta#_c survive up to quite high temperatures, with little observable change up to 1.5 T_c, and then gradually weakening and disappearing by 3 T_c. For the scalar and axial vector channels, serious modifications are induced by the hot medium already close to T_c, possibly dissociating the mesons by 1.1 T_c. (orig.)Available from TIB Hannover: RA 2999(03-215) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Charmonium at finite temperature

We study charmonium correlators and spectral functions at finite temperature within the quenched approximation using isotropic lattices with lattice spacing a"-"1=4.86 GeV and 9.72 GeV. Although we observe some medium modifications of the ground state charmonium spectral function above deconfinement, we find that ground state charmonia (J/#psi# and #eta#_c) exist in the deconfined phase at least up to temperatures as high as 1.5T_c. P-wave charmonia (#chi#_c) on the other hand are dissociated already at 1.12T_c. (orig.)Available from TIB Hannover: RA 2999(03-119) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Charmonium systems after the deconfinement transition

The behavior of charmonia after the deconfinement transition is investigated on quenched lattices. Analysis of temporal correlators on fine lattices at temperatures upto 3 T_c show that the J/#psi# and #eta#_c survive the deconfinement transition with little significant changes, and survive as bound states at least upto 2.25 T_c. The spatially excited #chi#_c, states suffer serious system modifications, maybe dissolution, already a little above T_c. (orig.)SIGLEAvailable from TIB Hannover: RA 08919(04-049) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman