Bottomonium transport in the sQGP at RHIC and the LHC

Abstract

Bottomonium transport is studied in heavy-ion collisions at RHIC and the LHC by implementing a kinetic rate equation into (3+1)D viscous hydrodynamic simulations of an expanding quark-gluon plasma (QGP). The two main transport parameters are the inelastic reaction rates and equilibrium limits for each individual bottomonium state, $Y$. The former are taken from the thermodynamic $T$-matrix formalism with recent constraints from lattice-QCD and including interference effects and in-medium binding energies, resulting in large rates characteristic of a strongly coupled QGP. The equilibrium limits are evaluated from pertinent in-medium bottomonium and bottom-quark masses. The calculation of observables includes a total of nine $Y$ states (up to 3$S$ and 2$P$) with a feed-down matrix estimated from vacuum branching fractions. At the LHC, the large reaction rates rapidly suppress the initial population of excited states, rendering regeneration their main source even in rather peripheral collisions, while for the more strongly bound ground state $\Upsilon(1S)$, a significant primordial component survives in central collisions. On the other hand, at RHIC energies, regeneration is overall a smaller effect. Together with effects from nuclear absorption, this offers an explanation for the experimental observation that $\Upsilon(1S)$ production at RHIC and the LHC is of comparable magnitude despite the significantly higher temperatures reached in the QGP at the LHC.