1,631 research outputs found

    Gluon saturation effects on J/Psi production in heavy ion collisions

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    We discuss a novel mechanism for J/Psi$ production in nuclear collisions arising due to the high density of gluons. We demonstrate that gluon saturation in the colliding nuclei is a dominant source of J/Psi suppression and can explain its experimentally observed rapidity and centrality dependence.Comment: Contribution to the "Quark Matter 2009" Proceeding

    Experimental study of local strong parity violation in relativistic nuclear collisions

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    Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created in relativistic heavy ions collisions. These domains are predicted to lead to charge separation along the system orbital momentum of the system created in non-central collisions. Three-particle mixed harmonics azimuthal correlator is a \P even observable but directly sensitive to the charge separation effect. Using this observable to analyze Au+Au and Cu+Cu collisions at sNN=200\sqrt{s_{NN}}=200 and 62 GeV, STAR detects a signal consistent with several of the theoretical expectations. Possible contributions from effects not related to parity violation are studied with existing event generators, which fail to describe the data. Future directions in studying the effect are discussed.Comment: Proceedings, plenary invited talk at Quark Matter 2009 Conference, Knoxville, Tennessee. One reference added. Final versio

    J/\psi Suppression in Pb+Pb Collisions: A New Look at Hadrons vs. Plasma

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    A reexamination of hadronic comover scattering indicates that this mechanism cannot explain the observed ψ\psi suppression in Pb+Pb interactions. The possibility of quark-gluon plasma formation is therefore considered.Comment: Calculations redone, figures updated, conclusions unchanged, to be published in Phys. Lett. B. 13 pages, LaTeX, uses epsf style, 4 figure

    Broken scale invariance, massless dilaton and confinement in QCD

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    Classical conformal invariance of QCD in the chiral limit is broken explicitly by scale anomaly. As a result, the lightest scalar particle (scalar glueball, or dilaton) in QCD is not light, and cannot be described as a Goldstone boson. Nevertheless basing on an effective low-energy theory of broken scale invariance we argue that inside the hadrons the non-perturbative interactions of gluon fields result in the emergence of a massless dilaton excitation (which we call the "scalaron"). We demonstrate that our effective theory of broken scale invariance leads to confinement. This theory allows a dual formulation as a classical Yang-Mills theory on a curved conformal space-time background. Possible applications are discussed, including the description of strongly coupled quark-gluon plasma and the spin structure of hadrons.Comment: 18 pages, 2 figures; v2: fixed numerous typo

    Heavy quarks and QCD matter

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    I present recent results on the theory of QCD matter production in high energy heavy ion collisions and on the interactions of heavy quarks in such environment. The centrality and rapidity dependence of hadron production is evaluated in semi--classical approach. The energy loss of heavy quarks in matter is computed. The heavy--to--light meson ratio (e.g., D/pion) at moderate transverse momenta is demonstrated to be both sensitive to the density of color charges in the medium and infrared stable.Comment: 10 pages, 3 figures; invited talk at the international conference on "Statistical QCD", August 26-30, 2001, Bielefel

    RHIC data and small x physics

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    This is a short review of some RHIC results that have been most important for the small x physics community. We discuss saturation effects in deuteron-gold collisions, particle production in gold-gold collisions and some effects of the large "glasma" field configurations in the early stages of the collision.Comment: 6 pages, 7 figures, uses espcrc2.sty. Talk at the International Symposium on Very High Energy Cosmic Ray Interactions, Paris, France, September 200

    J/ψJ/\psi suppression in heavy ion collsions and the QCD phase transition

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    We suggest that the new regime of J/ψJ/\psi suppression in Pb-Pb collisions found by the NA50 experiment at CERN is the result of non-trivial space-time evolution due to specific behavior of the Equation of State (EOS) near the QCD phase transition. We also study another suppression channel, the conversion of J/ψJ/\psi into ηc\eta_c during the late cool hadronic stage, and find it rather inefficient.Comment: 10 pages, 3 figure

    Signatures of the Color Glass Condensate in J/Psi production off nuclear targets

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    We consider the J/Psi production in proton (deuteron) -- nucleus collisions at high energies. We argue that the production mechanism in this case is different from that in pp collisions due to gluon saturation in the nucleus and formation of the Color Glass Condensate. At forward rapidities (in the proton fragmentation region), the production of J/Psi is increasingly suppressed both as a function of rapidity and centrality. On the other hand, at backward rapidities at RHIC (in the fragmentation region of the nucleus) the coherent effects lead to a modest enhancement of the production cross section, with the nuclear modification factor R(J/Psi) increasing with centrality. We find that the J/Psi production cross section exhibits at forward rapidities the limiting fragmentation scaling established previously for soft processes; in the energy range studied experimentally, it manifests itself as an approximate "xF scaling".Comment: 23 pages, 9 figure

    High energy pA collisions in the Color Glass Condensate approach

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    We present a brief review of phenomenological applications of the gluon saturation approach to the proton-nucleus collisions at high energies.Comment: To appear in the proceedings of 2nd International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions June 9-16, 2006, Asilomar Conference Grounds, Pacific Grove, Californi