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Register a new userQuarkonium in Heavy Ion Collisions -- high-energy multiple scattering of quark pair in nuclei
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H. Fujii
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Quarkonium suppression in heavy ion collisions is a potential signature of the formation of the quark-gluon plasma. After a very brief review of the J/psi result at CERN, we restrict our discussion to the effects of the high-energy multiple scattering of the quark pair in the colliding nuclei.
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Quarkonium production in high-energy proton (deuteron)-nucleus collisions is investigated in the color glass condensate framework. We employ the color evaporation model assuming that the quark pair produced from dense small-x gluons in the nuclear target bounds into a quarkonium outside the target. The unintegrated gluon distribution at small Bjorken x in the nuclear target is treated with the Balitsky-Kovchegov equation with running coupling corrections. For the gluons in the proton, we examine two possible descriptions, unintegrated gluon distribution and ordinary collinear gluon distribution. We present the transverse momentum spectrum and nuclear modification factor for J/psi production at RHIC and LHC energies, and those for Upsilon(1S) at LHC energy, and discuss the nuclear modification factor and the momentum broadening by changing the rapidity and the initial saturation scale.
Modifications to quark and antiquark fragmentation functions due to quark-quark (antiquark) double scattering in nuclear medium are studied systematically up to order cal{O}(alpha_{s}^2)$ in deeply inelastic scattering (DIS) off nuclear targets. At the order $cal{O}(alpha_s^2)$, twist-four contributions from quark-quark (antiquark) rescattering also exhibit the Landau-Pomeranchuck-Midgal (LPM) interference feature similar to gluon bremsstrahlung induced by multiple parton scattering. Compared to quark-gluon scattering, the modification, which is dominated by $t$-channel quark-quark (antiquark) scattering, is only smaller by a factor of $C_F/C_A=4/9$ times the ratio of quark and gluon distributions in the medium. Such a modification is not negligible for realistic kinematics and finite medium size. The modifications to quark (antiquark) fragmentation functions from quark-antiquark annihilation processes are shown to be determined by the antiquark (quark) distribution density in the medium. The asymmetry in quark and antiquark distributions in nuclei will lead to different modifications of quark and antiquark fragmentation functions inside a nucleus, which qualitatively explains the experimentally observed flavor dependence of the leading hadron suppression in semi-inclusive DIS off nuclear targets. The quark-antiquark annihilation processes also mix quark and gluon fragmentation functions in the large fractional momentum region, leading to a flavor dependence of jet quenching in heavy-ion collisions.
Recent lattice QCD data on higher order susceptibilities of Charm quarks provide the opportunity to explore Charm quark equilibration in the early quark gluon plasma (QGP) phase. Here, we propose to use the lattice data on second and fourth order net Charm susceptibilities to infer the Charm quark equilibration temperature and the corresponding volume, in the early QGP stage, via a combined analysis of experimentally measured multiplicity fluctuations. Furthermore, the first perturbative results for the second and fourth order Charm quark susceptibilities and their ratio are presented.
Modelling Quark-Gluon Plasma formation and decay in high energy heavy ion reactions is presented in a framework of a multi-module setup. The collective features, governing the equlibrated fluid dynamical stages of the model are emphasized. Flow effects formed from the initial conditions are discussed. Particular attention is given to the improvement of the final hadronization and freeze-out part of the reaction which has strong effects on the observables.
The electromagnetic process of bound-free electron pair production in heavy-ion collisions at high energies is reviewed. The importance of this process for producing secondary beams is outlined. Single free electron pair production is presented, and the bound-free pair production process is introduced. Double pair production is discussed, and an estimate of the bound-free pair constrained photon-photon luminosity is given.
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