Measurements of $\Upsilon$ Production and Nuclear Modification Factor at STAR

TL;DR

This paper reports measurements of Upsilon meson production in different collision systems at RHIC, providing insights into quark-gluon plasma effects and cold nuclear matter influences through nuclear modification factors.

Contribution

It presents new Upsilon cross section measurements in Au+Au, p+p, and d+Au collisions, offering comprehensive data on hot and cold nuclear matter effects at RHIC energies.

Findings

Observation of suppression in Upsilon production in Au+Au collisions.

Comparison of nuclear modification factors across collision systems.

Enhanced understanding of QGP signatures and cold nuclear matter effects.

Abstract

Thermal suppression of quarkonium production in heavy-ion collisions, due to Debye screening of the quark-antiquark potential, has been proposed as a clear signature of Quark-Gluon Plasma (QGP) formation. At RHIC energies, the $\Upsilon$ meson is a clean probe of the early system due to negligible levels of enhancement from \bbbar recombination and non-thermal suppression from co-mover absorption. We report on our measurement of the $\Upsilon \to e^+ e^-$ cross section in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. We compute the Nuclear Modification Factor by comparing these results to new p+p measurements from 2009 (21 pb$^{-1}$ in 2009 compared to 7.9 pb$^{-1}$ in 2006). In order to have a complete assessment of both hot and cold nuclear matter effects on Upsilon production we also report on results from d+Au collisions.