# Color Screening and Regeneration of Bottomonia in High-Energy Heavy-Ion Collisions

## TL;DR

This paper studies bottomonium production and suppression in high-energy heavy-ion collisions, incorporating medium effects, regeneration, and transport models to better understand QCD interactions in hot dense matter.

## Contribution

It introduces an improved kinetic-rate equation approach with temperature-dependent effects, resonance states, and lattice-QCD equations of state, enhancing predictions of bottomonium observables.

## Key findings

- $$ Upsilon(1S) suppression as a probe of in-medium QCD force properties.
- $$ Regeneration significantly influences bottomonium yields, especially for excited states.
- $$ Transverse-momentum spectra and elliptic flow are sensitive to regeneration and medium effects.

## Abstract

The production of ground-state and excited bottomonia in ultrarelativistic heavy-ion collisions is investigated within a kinetic-rate equation approach including regeneration. We augment our previous calculations by an improved treatment of medium effects, with temperature-dependent binding energies and pertinent reaction rates, $B$-meson resonance states in the equilibrium limit near the hadronization temperature, and a lattice-QCD based equation of state for the bulk medium. In addition to the centrality dependence of the bottomonium yields we compute their transverse-momentum ($p_T$) spectra and elliptic flow with momentum-dependent reaction rates and a regeneration component based on $b$-quark spectra from a nonperturbative transport model of heavy-quark diffusion. The latter has noticeable consequences for the shape of the bottomonium $p_T$ spectra. We quantify how uncertainties in the various modeling components affect the predictions for observables. Based on this we argue that the $\Upsilon(1S)$ suppression is a promising observable for mapping out the in-medium properties of the QCD force, while $\Upsilon(2S)$ production can help to quantify the role of regeneration from partially thermalized $b$ quarks.