Holographic Picture of Heavy Vector Meson Melting

TL;DR

This paper uses an extended holographic model to analyze the thermal dissociation of heavy vector mesons like bottomonium and charmonium, revealing how different states melt at various temperatures in a quark-gluon plasma.

Contribution

It introduces a finite-temperature extension of a soft wall AdS/QCD model that accurately predicts decay constants and masses of heavy mesons, and analyzes their melting behavior in thermal medium.

Findings

Higher excitations melt at lower temperatures.

Bottomonium 1S state survives at temperatures above deconfinement.

Spectral functions show clear melting transitions for all states.

Abstract

The fraction of heavy vector mesons produced in a heavy ion collision, as compared to a proton proton collision, serves as an important indication of the formation of a thermal medium, the quark gluon plasma. This sort of analysis strongly depends on understanding the thermal effects of a medium like the plasma on the states of heavy mesons. In particular, it is crucial to know the temperature ranges where they undergo a thermal dissociation, or melting. AdS/QCD models are know to provide an important tool for the calculation of hadronic masses, but in general are not consistent with the observation that decay constants of heavy vector mesons decrease with excitation level. It has recently been shown that this problem can be overcome using a soft wall background and introducing an extra energy parameter, through the calculation of correlation functions at a finite position of anti-de Sitter space. This approach leads to the evaluation of masses and decay constants of S wave quarkonium states with just one flavor dependent and one flavor independent parameters. Here we extend this more realistic model to finite temperatures and analyse the thermal behavior of the states $1S, 2S$ and $ 3S$ of bottomonium and charmonium. The corresponding spectral function exhibits a consistent picture for the melting of the states where, for each flavor, the higher excitations melt at lower temperatures. We estimate for these six states, the energy ranges in which the heavy vector mesons undergo a transition from a well defined peak in the spectral function to complete melting in the thermal medium. A very clear distinction between the heavy flavors emerges, with bottomonium state $\Upsilon (1S)$ surviving deconfinemet transition at temperatures much larger than the critical deconfinement temperature of the medium.