Measurements of ϒ Production and Nuclear Modification Factor at STAR

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 ϒ meson is a clean probe of the early system due to negligible levels of enhancement from b b ¯ recombination and non-thermal suppression from co-mover absorption. We report on our measurement of the ϒ → e + e − cross section in Au+Au collisions at s N N = 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.