γ production in p+p and Pb+Pb collisions at √NN=2.76 TeV

The heavy ion collisions are performed to study the interaction of matter at extreme temperatures and densities where it is expected to be in the form of Quark Gluon Plasma (QGP), a state where color degrees of freedom are dominant. One of the expected signal of this phase is the suppression of quarkonium states, both from the charmonium (J/ψ , ψ, ξc, etc.) and bottomonium families (γ(1S, 2S, 3S), ξb, etc) due to the color screening produced by the surrounding light quarks and gluons. The suppression is predicted to occur above a critical temperature Tc, sequentially, in order of the binding energy. Since the γ(1S) is the strongest bound state among all quarkonia, it is expected to be the last to melt in the QGP. Examples of dissociation temperatures are given in reference and are < 1 Tc, 1.2 Tc, and more than 2 Tc for the γ(3S), γ(2S) and γ(1S) respectively