Deconfinement as an entropic self-destruction: a solution for the quarkonium suppression puzzle?

Abstract: The entropic approach to dissociation of bound states immersed in strongly coupled systems is developed. In such systems, the excitations of the bound state are often delocalized and characterized by a large entropy, so that the bound state is strongly entangled with the rest of the statistical system. If this entropy $S$ increases with the separation $r$ between the constituents of the bound state, $S = S(r)$, then the resulting entropic force $F = T\ {\partial S}/{\partial r}$ ($T$ is temperature) can drive the dissociation process. As a specific example, we consider the case of heavy quarkonium in strongly coupled quark-gluon plasma, where lattice QCD indicates a large amount of entropy associated with the heavy quark pair at temperatures $0.9\ T_c \leq T \leq 1.5\ T_c$ ($T_c$ is the deconfinement temperature); this entropy $S(r)$ grows with the inter-quark distance $r$. We argue that the entropic mechanism results in an anomalously strong quarkonium suppression in the temperature range near $T_c$. This "entropic self-destruction" may thus explain why the experimentally measured quarkonium nuclear modification factor at RHIC (lower energy density) is smaller than at LHC (higher energy density), possibly resolving the "quarkonium suppression puzzle" - all of the previously known mechanisms of quarkonium dissociation operate more effectively at higher energy densities, and this contradicts the data. Moreover, we find that near $T_c$ the entropic force leads to delocalization of the bound hadron states; we argue that this delocalization may be the mechanism underlying deconfinement.