Measuring the Upsilon Nuclear Modification Factor at STAR

TL;DR

This paper measures the nuclear modification factor RAA for Upsilon mesons in heavy ion collisions at STAR, providing insights into quark-gluon plasma effects and quarkonium suppression mechanisms.

Contribution

It presents the first measurement of Upsilon RAA at STAR, analyzing suppression patterns and centrality dependence in Au+Au collisions at 200 GeV.

Findings

Upsilon suppression observed in heavy ion collisions.

Centrality dependence of RAA quantified.

Results constrain models of QGP effects on quarkonia.

Abstract

Suppression of quarkonia in heavy ion collisions with respect to proton-proton collisions due to the Debye screening of the potential between the heavy quarks was hypothesized to be a signature of the Quark Gluon Plasma (QGP). However, other effects besides Debye screening, such as the statistical recombination of quark anti-quark heavy flavor pairs, or co-mover absorption can also affect quarkonia production in heavy ion collisions. Quantifying the suppression of an entire family of quarkonium mesons can give us a model dependent constraint on the temperature. The suppression of Upsilon can be quantified by calculating the Nuclear Modification factor, RAA, which is the ratio of the production in Au+Au collisions to the production in p+p scaled by the number of binary collisions. We present our results for mid-rapidity Upsilon(1S+2S+3S) production in p+p and Au+Au collisions at sqrt(sNN) = 200 GeV. The centrality dependence of RAA will be shown for the combined Upsilon(1S+2S+3S) yield.