Speaker
Dr
Rongrong Ma
(Brookhaven National Laboratory)
Description
Measurements of quarkonium production in heavy-ion collisions have played an essential role in understanding the properties of the Quark Gluon Plasma (QGP) created in such collisions. In particular, $J/\psi$ suppression in the medium has been proposed as a direct probe of the QGP formation, where quarks and gluons are the relevant degrees of freedom. However, regeneration of $J/\psi$ from uncorrelated $c$ and $\bar{c}$ quarks in the medium adds extra complications to the interpretation of $J/\psi$ suppression. The measurement of the second order harmonic coefficient ($v_{2}$) for $J/\psi$ would help disentangle different production mechanisms since the regenerated $J/\psi$ is expected to inherit the flow of the charm quarks while the primordial $J/\psi$ should have almost zero $v_{2}$. On the other hand, the contribution from regeneration to $\Upsilon$, $b\bar{b}$ bound states, is much smaller at RHIC energies, making them ideal probes to study the color-screening feature. In early 2014, the Muon Telescope Detector (MTD), designed to trigger on and identify muons based on precise timing information, was fully installed in STAR at mid-rapidity. Due to the low trigger threshold on muon $p_{\rm{T}}$, the MTD trigger has a relatively high efficiency for low $p_{\rm{T}}$ $J/\psi$, where the regeneration contribution is expected to be the largest. Moreover, the MTD opens the door for separating different $\Upsilon$ states for the first time at STAR as the Bremsstrahlung radiation for muons is much smaller compared to electrons. In this talk, we present the measurements of $J/\psi$ suppression, quantified as the nuclear modification factor $R_{\rm{AA}}$, and $v_{2}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV down to zero $p_{\rm{T}}$. These measurements bring extra insights into the $J/\psi$ production mechanism in heavy-ion collisions. Furthermore, the measurement of different $\Upsilon$ states is explored within the precision of the available statistics.
| On behalf of collaboration: | STAR |
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Primary author
Dr
Rongrong Ma
(Brookhaven National Laboratory)
