Bottomonium production in heavy-ion collisions at STAR

TL;DR

This paper reports on bottomonium suppression patterns in heavy-ion collisions at STAR, revealing significant suppression of the ground state and hints of incomplete suppression of excited states, supporting sequential dissociation models.

Contribution

It provides new measurements of bottomonium states in U+U collisions at STAR, extending understanding of quarkonium suppression at higher energy densities and participant nucleons.

Findings

Upsilon(1S) is significantly suppressed in central Au+Au collisions.

Upsilon(1S) suppression extends to U+U collisions with higher energy density.

Hint that excited states are not fully suppressed in U+U collisions.

Abstract

Bottomonium measurements provide unique insight into hot and cold nuclear matter effects present in the medium that is formed in high-energy heavy-ion collisions. Recent STAR results show that in $\sqrt{s_{NN}}$ = 200 GeV central Au+Au collisions the $\Upsilon$(1S) state is suppressed more than if only cold nuclear matter effects were present, and the excited state yields are consistent with a complete suppression. In 2012, STAR also collected 263.4 $\mu$b$^{-1}$ high-energy-electron triggered data in U+U collisions at $\sqrt{s_{NN}}$= 193 GeV. Central U+U collisions, with an estimated 20% higher energy density than in central Au+Au data, extend the $\Upsilon$(1S+2S+3S) and Upsilon(1S) nuclear modification trends observed in Au+Au towards higher number of participant nucleons, and confirm the suppression of the $\Upsilon$(1S) state. We see a hint with 1.8 sigma significance that the $\Upsilon$(2S+3S) excited states are not completely suppressed in U+U collisions. These data support the sequential in-medium quarkonium dissociation picture and favor models with a strong $q\bar{q}$ binding.