Measurements of $Υ$ Production and Nuclear Modification Factor at STAR

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 $Υ$ 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 $Υ\to e^+ e^-$ 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.

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