Properties of Quarkonia at T_c

TL;DR

This paper investigates how the spectral properties of quarkonia, especially J/psi, change near the QCD critical temperature T_c, revealing abrupt modifications in gluon condensates and quarkonium characteristics due to the phase transition.

Contribution

It provides a detailed analysis of the temperature dependence of gluon condensates near T_c and links these changes to observable modifications in quarkonium masses and widths using QCD sum rules.

Findings

Electric condensate increases abruptly above T_c

J/psi mass and width change by over 100 MeV near T_c

Magnetic condensate remains nearly constant across T_c

Abstract

We discuss how the spectral changes of quarkonia at T_c can reflect the ``critical'' behaviour of QCD phase transition. Starting from the temperature dependencies of the energy density and pressure from lattice QCD calculation, we extract the temperature dependencies of the scalar and spin 2 gluon condensates near T_c. We also parameterize these changes into the electric and magnetic condensate near T_c. While the magnetic condensate hardly changes across T_c, we find that the electric condensate increases abruptly above T_c. Similar abrupt change is also seen in the scalar condensate. Using the QCD second-order Stark effect and QCD sum rules, we show that these sudden changes induce equally abrupt changes in the mass and width of J/psi, both of which are larger than 100 MeV at slightly above T_c.