J/ψProduction in Quark-Gluon Plasma

Abstract

We study J/ψ production at RHIC and LHC energies with both initial production and regeneration. We solve the coupled set of transport equation for the J/ψ distribution in phase space and the hydrodynamic equation for evolution of quark-gluon plasma. At RHIC, continuous regeneration is crucial for the J/ψ momentum distribution while the elliptic flow is still dominated by initial production. At LHC energy, almost all the initially created J/ψs are dissociated in the medium and regeneration dominates the J/ψ properties. 12.38.Mh, 24.85.+p The goal of high-energy nuclear collisions is to identify and study the equation of state of the Quark-Gluon Plasma (QGP) which is believed to exist at the early stage of our universe [1]. In √ s N N = 200 GeV Au + Au collisions, the observations of jet-quenching [2] and collective flow have demonstrated the formation of hot and dense matter with partonic collectivity [3,4]. Local thermalization of the system created in heavy ion collisions is yet to be tested. Heavy flavors including charm and bottom quarks are powerful tools [5] for studying the early collision dynamics because their masses are much larger than possible excitation, temperature for example, of the system created in collisions at RHIC. Recent results have shown that heavy flavors are all produced in the initial collisions [6,7]. Therefore, studying open charm and charmonium production will yield important information on the properties of QGP. The J/ψ is a particularly sensitive probe of the early stages because its survial probability depends on the environment. Lattice gauge theory calculations have indicated that J/ψs do exist above the critical temperature [8,9].The J/ψ suppression was first proposed as a direct signature to identify the QGP formation twenty years ago [10]. Besides the normal suppression induced by nuclear absorption, the J/ψs initially produced by hard processes are anomalously suppressed [11,12,13,14,15,16,17] by interactions in the hot medium. While charm quark production at the SPS is expected to be small, there are more than 10 cc pairs produced in a central Au + Au collision at RHIC, and is probably more than 200 pairs at the LHC [18]. These uncorrelated charm quark pairs in the QGP can be recombined to form J/ψs. Obviously, regeneration will enhance the J/ψ yield and alter its momentum spectra. Recently, the regeneration approach for J/ψ production at RHIC has been widely discussed with different models, such as thermal production on the hadronizaton hypersurface according to statistic law [19,20,21], the coalescence mechanism [22] and the kinetic model [23,24] which considers continuous J/ψ regeneration in a QGP.The medium created in high-energy nuclear collisions evolves dynamically. In order to extract information about the medium by analyzing the J/ψ distributions, both the hot and dense medium and the J/ψ production processes must be treated dynamically. In this Letter, we treat continuous regeneration of the J/ψ in a QGP self-consistently, including hydrodynamic evolution of t...

Negative elliptic flow of J/ψ’s: A qualitative signature for charm collectivity at RHIC

“…Due to the large error bars this has to be verified when more precise data is available. Note that our present findings are different from previous approaches that assume incomplete thermalization of the charm [18][19][20][21]. We also verified our findings within a Boltzmann approach to coalescence [20] using our parametrizations and received similar results.…”

Charmonium production in relativistic heavy-ion collisions

“…Since J/ψ suppression was first suggested by Matsui and Satz as a signature of quark-gluon plasma (QGP) formation in relativistic heavy-ion collisions [1], there have been many experimental [2,3] and theoretical studies [4][5][6][7][8] on this very interesting phenomenon; see, e.g., Refs. [9,10] for a recent review.…”

Quarkonia production in the STAR experiment

“…At p T > 2 GeV/c v 2 is consistent with zero. Compared to different model predictions [17][18][19][20], data disfavor the scenario that J/ψ with p T > 2 GeV/c are dominantly produced by recombination (coalescence) from thermalized cc pairs. [12] and high-p T (> 5 GeV/c) [13] regions.…”

“…Panel (d) shows also p + p results as stars and Cu+Cu results as triangles. Right: J/ψ v 2 in Au+Au collisions at √ s NN = 200 GeV at mid-rapidity in 0-80% central events [16] with different model predictions ( [17][18][19][20]). The gray boxes represent a non-flow estimation.…”