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

Understand

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).