J/psi and eta_c in the nuclear medium: QCD sum rule approach

Abstract

We investigate the masses of the lowest c\bar{c} states, the J/psi and eta_c, in nuclear matter using QCD sum rules. Up to dimension four, the differences between the operator product expansions in vacuum and in medium arise from the density-dependent change in the gluon condensate and from a new contribution proportional to the nucleon expectation value of the twist-2 gluon operator. Both terms together give an attractive shift of about 5-10 MeV to the J/psi and eta_c masses in nuclear matter.

Comments: 4 pages, ReVTeX, 2 figures in eps, submitted to Phys.Rev.Lett. Updated version: an error in eqn. 4 has been corrected, several references have been added, figures have been revised