Critical behavior of charmonia across the phase transition: A QCD sum rule approach

TL;DR

This study uses QCD sum rules to analyze how the masses and widths of charmonia, specifically J/psi and eta_c, change across the QCD phase transition, revealing sudden spectral modifications near the critical temperature.

Contribution

It provides a novel analysis of medium-induced modifications of charmonia across the QCD phase transition using lattice-informed gluon condensates within the QCD sum rule framework.

Findings

Charmonia masses decrease by a few hundred MeV above Tc

Widths broaden to about 100 MeV near and above Tc

Spectral properties change abruptly across the critical temperature

Abstract

We investigate medium-induced change of mass and width of J/psi and eta_c across the phase transition in hot gluonic matter using QCD sum rules. In the QCD sum rule approach, the medium effect on heavy quarkonia is induced by the change of both scalar and twist-2 gluon condensates, whose temperature dependences are extracted from the lattice calculations of energy density and pressure. Although the stability of the operator product expansion side seems to break down at T > 1.06Tc for the vector channel and T>1.04Tc for the pseudoscalar channel, we find a sudden change of the spectral property across the critical temperature Tc, which originates from an equally rapid change of the scalar gluon condensate characterized by e-3p. By parameterizing the ground state of the spectral density by the Breit-Wigner form, we find that for both J/psi and eta_c, the masses suddenly decrease maximally by a few hundreds of MeV and the widths broaden to ~100 MeV slightly above Tc. Implications for recent and future heavy ion experiments are discussed. We also carry out a similar analysis for charmonia in nuclear matter, which could serve as a testing ground for observing the precursor phenomena of the QCD phase transition. We finally discuss the possibility of observing the mass shift at nuclear matter at the FAIR project at GSI.