Showing papers on "Color-glass condensate published in 2006"
TL;DR: In this article, the authors discuss high energy hadronic collisions within the theory of the color glass condensate and point out that the initial electric and magnetic fields produced in such collisions are longitudinal, which leads to a novel string like description of the collisions, and a large Chern-Simons charge density made immediately after the collision.
431 citations
TL;DR: In this paper, a hybrid approach which combines early ideal fluid dynamical evolution with late hadronic rescattering was used to demonstrate strong dissipative effects from the late rescattering stage on the elliptic flow coefficient v 2 ( η, b ) in Au + Au collisions at s = 200 A GeV as a function of pseudorapidity η and impact parameter b.
368 citations
TL;DR: In this paper, a review of parton saturation/color glass condensate physics in the context of deuteron-gold (d + Au ) collisions at RHIC is presented.
324 citations
TL;DR: In this paper, one loop corrections to single-inclusive particle production in parton-nucleus scattering at high energies are considered, treating the target nucleus as a color glass condensate.
259 citations
TL;DR: Blaizot et al. as mentioned in this paper considered the effects of small x quantum evolution on pair production in high energy pA collisions and provided results for pair production as a function of the invariant mass of pairs, the pair momenta, and the atomic mass number A.
123 citations
TL;DR: In this article, it was shown that the initial energy density produced in an ultrarelativistic heavy ion collision can, in the color glass condensate framework, be factorized into a product of the integrated gluon distributions of the nuclei.
110 citations
TL;DR: The eccentricity in coordinate space at midrapidity of the overlap zone in high-energy heavy-ion collisions predicted by the ENF formalism is generically larger than expected from scaling with the number of participants as mentioned in this paper.
Abstract: The eccentricity in coordinate space at midrapidity of the overlap zone in high-energy heavy-ion collisions predicted by the ${k}_{\ensuremath{\perp}}$-factorization formalism is generically larger than expected from scaling with the number of participants. We provide a simple qualitative explanation of the effect which shows that it is not caused predominantly by edge effects. We also show that it is quite insensitive to ``details'' of the unintegrated gluon distribution functions such as the presence of leading-twist shadowing and of an extended geometric scaling window. The larger eccentricity increases the azimuthal asymmetry of high transverse momentum particles. Finally, we point out that the longitudinal structure of the color glass condensate initial condition for hydrodynamics away from midrapidity is nontrivial but requires understanding of large-$x$ effects.
108 citations
TL;DR: In this paper, the anomalous dimension of the small-x gluon distribution of RHIC deuteron-nucleus and HERA DIS phenomenology is investigated.
85 citations
TL;DR: In this paper, the authors consider the production of J / Ψ in proton (deuteron)−nucleus collisions at high energies and show 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.
77 citations
TL;DR: In this article, it was shown that the early elliptic flow in heavy ion collisions (unlike multiplicity distributions) is sensitive to the universality of the saturation scale in high-energy QCD, and that a saturation scale proportional to the nuclear thickness function leads to a smaller eccentricity, albeit still larger than the value used in hydrodynamic models.
Abstract: Recent estimates that color glass condensate initial conditions may generate a larger initial eccentricity for noncentral relativistic heavy ion collisions (relative to the initial eccentricity assumed in earlier hydrodynamic calculations) have raised the possibility of a higher bound on the viscosity of the qark gluon plasma. We show that this large initial eccentricity results in part from a definition of the saturation scale as proportional to the number of nucleons participating in the collision. A saturation scale proportional to the nuclear thickness function (and therefore independent of the probe) leads to a smaller eccentricity, albeit still larger than the value used in hydrodynamic models. Our results suggest that the early elliptic flow in heavy ion collisions (unlike multiplicity distributions) is sensitive to the universality of the saturation scale in high-energy QCD.
62 citations
TL;DR: In this paper, the authors analyze the universality of these dipole cross section parameterizations and verify that they are not able to describe the HERA and RHIC data simultaneously.
TL;DR: In this article, the effects of modifying the behavior of the gluon distribution function at very small values of Bjorken x in the DGLAP evolution equation were numerically investigated.
Abstract: The cross section for ultrahigh energy neutrino-nucleon scattering is very sensitive to the parton distributions at very small values of Bjorken x (x{<=}10{sup -4}) We numerically investigate the effects of modifying the behavior of the gluon distribution function at very small x in the DGLAP evolution equation We then use the Color Glass Condensate formalism to calculate the neutrino-nucleon cross section at ultrahigh energies and compare the result with those based on modification of DGLAP evolution equation
TL;DR: In this article, the photoproduction of heavy quarks and vector mesons in the coherent proton-nucleus (pA) interactions for RHIC and LHC energies is studied and the integrated cross section and rapidity distribution are estimated using the color glass condensate (CGC) formalism.
Abstract: In this paper we study the photoproduction of heavy quarks and vector mesons in the coherent proton-nucleus (pA) interactions for RHIC and LHC energies and analyze if these processes can be used to determine the QCD dynamics at high energies. The integrated cross section and rapidity distribution are estimated using the color glass condensate (CGC) formalism. A comparison with the linear dynamics predictions is also presented. Our results indicate that the nonlinear dynamics can be proven in those reactions, which are well suited for studing saturation effects.
TL;DR: In this paper, the Pomeron loop effects in the evolution equations for the Color Glass Condensate were studied for particle production in asymmetric, "dilute-dense" collisions, where a dilute projectile scatters off a dense target whose gluon distribution is highly evolved.
TL;DR: In this paper, the authors studied the SU(2) 3+1-D Yang-Mills equations for matter produced in a high-energy heavy-ion collision and showed that the growth of the amplitude of fluctuations is due to a non-Abelian Weibel instability, the scale of which is set by dynamically generated plasmon mass.
Abstract: Based on our work hep-ph/0510121, we discuss further the numerical study of classical SU(2) 3+1-D Yang-Mills equations for matter produced in a high-energy heavy-ion collision. The growth of the amplitude of fluctuations as exp(Γ\( \sqrt{{g^2\mu\tau}}\)) (where g2μ is a scale arising from the saturation of gluons in the nuclear wave function) is shown to be robust over a wide range of initial amplitudes that violate boost invariance. We argue that this growth is due to a non-Abelian Weibel instability, the scale of which is set by a dynamically generated plasmon mass. We discuss the relation of Γ to the prediction from kinetic theory.
TL;DR: In this paper, an evolution equation for the Bjorken dependence of diffractive dissociation on hadrons and nuclei at high energies is presented, based on a technique used by Weigert to describe interjet energy flow.
Abstract: We present an evolution equation for the Bjorken $x$ dependence of diffractive dissociation on hadrons and nuclei at high energies. We extend the formulation of Kovchegov and Levin by relaxing the factorization assumption used there. The formulation is based on a technique used by Weigert to describe interjet energy flow. The method can be naturally extended to other exclusive observables.
TL;DR: In this article, the color glass condensate formalism was applied to photon + hadron production cross section in high energy deuteron (proton)-gold collisions at RHIC.
TL;DR: In this article, the authors considered single-inclusive forward pion production in high-energy proton-proton collisions at RHIC energies and derived a good baseline description of the transverse momentum distributions at high rapidity.
Abstract: We consider single-inclusive forward pion production in high-energy proton-proton collisions at RHIC energies. A good baseline description of the transverse momentum distributions at high rapidity is obtained within Mueller's dipole formalism with an anomalous dimension incorporating an "extended geometric scaling" window between the saturation and DGLAP regimes. We then formulate pion production for transversely polarized projectiles within the same approach. We assume that an azimuthal, spin-dependent asymmetry arises from the so-called Sivers effect and investigate the single transverse-spin asymmetry A(N) at 200 GeV and 500 GeV center-of-mass energy. A simple parametrization of the Sivers functions from the literature compares reasonably well with the high-energy STAR data if the overall normalization is scaled up by at least a factor of 2. The STAR data might therefore indicate that the Sivers effect is significantly stronger than thought so far. We also analyze higher-twist contributions to A(N) and find that they largely cancel.
TL;DR: In this paper, the authors examined in a systematic way whether the nuclear modification factor measured for d-Au collisions at RHIC may be explained by boosting the saturation momentum by an additional nuclear component as already shown in the literature.
TL;DR: In this paper, the two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged particles at mid-rapidity in d+Au and p+p collisions at the Relativistic Heavy Ion Collider were investigated.
Abstract: Deuteron-gold (d+Au) collisions at the Relativistic Heavy Ion Collider provide ideal platforms for testing QCD theories in dense nuclear matter at high energy. In particular, models suggesting strong saturation effects for partons carrying small nucleon momentum fraction (x) predict modifications to jet production at forward rapidity (deuteron-going direction) in d+Au collisions. We report on two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged hadrons at midrapidity in d+Au and p+p collisions at root s(NN)=200 GeV. Jet structures observed in the correlations are quantified in terms of the conditional yield and angular width of away-side partners. The kinematic region studied here samples partons in the gold nucleus with x similar to 0.1 to similar to 0.01. Within this range, we find no x dependence of the jet structure in d+Au collisions.
TL;DR: In this paper, the authors examined entropy production in relativistic U+U collisions on the basis of a color glass condensate (CGC) type picture as implemented in the Kharzeev-Levin-Nardi model (KLN).
TL;DR: In this article, the authors considered that the nucleus at high energies acts as an amplifier of the physics of high parton densities and estimated the nuclear structure function F2A(x,Q2), as well as the longitudinal and charm contributions, using a generalization for nuclear targets of the Iancu-Itakura-Munier model.
Abstract: Perturbative quantum chromodynamics (pQCD) predicts that the small-x gluons in a hadron wavefunction should form a color glass condensate (CGC), characterized by a saturation scale Qs(x,A), which is energy and atomic number dependent. In this paper, we study the predictions of CGC physics for electron-ion collisions at high energies. We consider that the nucleus at high energies acts as an amplifier of the physics of high parton densities and estimate the nuclear structure function F2A(x,Q2), as well as the longitudinal and charm contributions, using a generalization for nuclear targets of the Iancu–Itakura–Munier model that describes the ep HERA data quite well. Moreover, we investigate the behavior of the logarithmic slopes of the total and longitudinal structure functions in the kinematical region of the future electron-ion collider eRHIC.
TL;DR: In this paper, Kovchegov et al. showed that the success of hydrodynamic models in describing the quark-gluon system produced in heavy ion collisions could only be due to non-perturbative strong coupling effects.
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TL;DR: In this paper, the McLerran-Venugopalan model was used to estimate the gluon field at early times after the collision in the framework of the color glass condensate model.
Abstract: We calculate the classical gluon field created at early times in collisions of large nuclei at high energies. We find that the field is dominated by the longitudinal chromoelectric and chromomagnetic components. We estimate the initial energy density of this gluon field to be approximately 260 GeV/fm 3 at RHIC. sions of gold nuclei at √ sNN = 200 GeV energy densities far in excess of the critical value required for deconfine- ment (ǫc ≈ 2 GeV/fm 3 ) are reached (1). Furthermore, the partonic phase seems to be thermalized after a very short time τ0 < 1 fm/c. While the evolution of the quark gluon plasma in equilibrium can be described by rela- tivistic hydrodynamics (2), the initial soft interactions of the nuclei and the thermalization process before the time τ0 are still not completely understood. It has been argued that the initial dynamics for the collision of two very high energy nuclei is determined by a universal phase called the color glass condensate (CGC). This idea is based on gluon saturation at a scale Qs (3, 4, 5, 6, 7). Slowly evolving and randomly distributed color charges in the nuclei are the sources of this gluon field. A simple implementation is the McLerran-Venugopalan (MV) model (3, 4) in which the gluon field is given by the solution of the classical Yang-Mills equations. In this Letter we calculate the gluon field at early times after the collision in the framework of the McLerran- Venugopalan model. We use an expansion of the Yang- Mills equations in powers of the proper time τ. This is a near-field approximation which may be the most appro- priate use of the color glass condensate picture. We also estimate the initial energy density at the time of overlap of the nuclei using a simple model for the nuclear gluon distribution and coarse-graining methods to avoid ultra- violet (UV) singularities. More details and a discussion of applications will be provided elsewhere (8). In high energy collisions the two colliding nuclei are highly Lorentz contracted; therefore, the valence and large-x partons are described by infinitesimally thin sheets propagating on the light cone. Although each nu- cleus is color neutral as a whole, local color fluctuations do occur. At the moment of overlap, the color distribu- tions in nucleus 1 (+ light cone) and 2 (− light cone) are ρ1(x⊥) and ρ2(x⊥), respectively. We use light cone
28 Nov 2006
TL;DR: In this paper, the effects of modifying the behavior of the gluon distribution function at very small values of Bjorken x (x ⩽ 10−4) in the DGLAP evolution equation were investigated.
Abstract: The cross section for ultra‐high energy neutrino‐nucleon scattering is very sensitive to the parton distributions at very small values of Bjorken x (x ⩽ 10−4). We numerically investigate the effects of modifying the behavior of the gluon distribution function at very small x in the DGLAP evolution equation. We then use the Color Glass Condensate formalism to calculate the neutrino‐nucleon cross section at ultra‐high energies and compare the result with those based on modification of DGLAP evolution equation.
TL;DR: In this paper, it was shown that the apparent thermalization of quarks and gluons, leading to success of perfect fluid hydrodynamics in describing heavy-ion collisions at RHIC, can only be attributed to the non-perturbative QCD effects not captured by Feynman diagrams.
Abstract: We argue that isotropization and, consequently, thermalization of the system of gluons and quarks produced in an ultrarelativistic heavy-ion collision does not follow from Feynman diagram analysis to any order in the coupling constant. We conclude that the apparent thermalization of quarks and gluons, leading to success of perfect fluid hydrodynamics in describing heavy-ion collisions at RHIC, can only be attributed to the non-perturbative QCD effects not captured by Feynman diagrams. We proceed by modeling these non-pertrubative thermalization effects using viscous hydrodynamics. We point out that matching Color Glass Condensate inital conditions with viscous hydrodynamics leads to a continuous evolution of all the components of the energy-momentum tensor and, unlike the case of ideal hydrodynamics, does not give rise to a discontinuity in the longitudinal pressure. An important consequence of such a matching is a relationship between the thermalization time and shear viscosity: we observe that small viscosity leads to short thermalization time.
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TL;DR: In this article, it was shown that the average multiplicity can be computed to leading order in the coupling and (remarkably) to next-to-leading order as well.
Abstract: In the Color Glass Condensate (CGC) effective field theory, colliding sheets of Colored Glass form a strongly interacting, non-equilibrium state called the Glasma. How Colored Glass shatters to form the Glasma, the properties of the Glasma, and how the Glasma thermalizes into a Quark Gluon Plasma(QGP) are questions of central interest in understanding the properties of the strongly interacting matter produced in heavy ion collisions. We argue that these questions can be addressed in the framework of field theories with strong time dependent external sources. Albeit such field theories are non-perturbative for arbitrarily weak coupling, moments of the multiplicity distribution can be computed systematically in powers of the coupling constant. We demonstrate that the average multiplicity can be (straightforwardly) computed to leading order in the coupling and (remarkably) to next-to-leading order as well. We relate our formalism to results from previous 2+1 and 3+1 dimensional numerical simulations of the Glasma fields. The expanding Glasma is unstable; small fluctuations in the initial conditions grow exponentially with the square root of the proper time. Whether this explosive growth leads to early thermalization in heavy ion collisions requires at present a better understanding of these fluctuations on the light cone. In the final lecture, motivated by recent work of Bialas and Jezabek, we discuss the widely observed phenomenon of limiting fragmentation in the CGC framework.
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21 Apr 2006
TL;DR: In this article, the classical gluon field created at early times in collisions of large nuclei at high energies was calculated and the authors found that the field is dominated by the longitudinal chromoelectric and chromomagnetic components.
Abstract: We calculate the classical gluon field created at early times in collisions of large nuclei at high energies. We find that the field is dominated by the longitudinal chromoelectric and chromomagnetic components. We estimate the initial energy density of this gluon field to be approximately 260 GeV/fm$^3$ at RHIC.
TL;DR: In this paper, the nuclear modification ratio suppression in the dilepton rapidity spectra is verified for LHC energies at large transverse momentum, although not present at RHIC energies, showing the large saturation effects at LHC compared with the RHIC results.
TL;DR: In this article, the decoherence time of the ground state wave function of a nucleus in a high energy heavy ion collision was calculated and it was shown that this time is smaller or equal to 1/Q{sub s, where the saturation scale is defined within the color glass condensate model of parton saturation.
Abstract: We calculate the decoherence time of the ground state wave function of a nucleus in a high energy heavy ion collision. We define this time as the decay time of the ratio Tr D{sup 2}/(Tr D){sup 2} of traces of the density matrix D. We find that this time is smaller or equal to 1/Q{sub s}, where the saturation scale Q{sub s} is defined within the color glass condensate model of parton saturation. Our result supports the notion that the extremely rapid entropy production deduced for the early stage of heavy ion collisions at collider energies is to a large extent caused by the decoherence of the initial-state wave functions.