Showing papers on "Color-glass condensate published in 2015"
TL;DR: In this paper, the authors re-evaluate the production cross sections in the Color Glass Condensate framework, where the process is described by a large x gluon from the probe splitting into a quark pair and eikonally interacting with the target proton or nucleus.
Abstract: Inclusive production of $J/\psi$ mesons, especially at forward rapidities, is an important probe of small-x gluons in protons and nuclei. In this paper we re-evaluate the production cross sections in the Color Glass Condensate framework, where the process is described by a large x gluon from the probe splitting into a quark pair and eikonally interacting with the target proton or nucleus. Using a standard collinear gluon distribution for the probe and an up to date dipole cross section fitted to HERA data to describe the target we achieve a rather good description of the cross section in proton-proton collisions, although with a rather large normalization uncertainty. More importantly, we show that generalizing the dipole cross section to nuclei in the Glauber approach results in a nuclear suppression of $J/\psi$ production that is much closer to the experimental data than claimed in previous literature.
99 citations
TL;DR: The distribution of linearly polarized gluons of a dense target at small x is determined by solving the Balitsky-Jalilian-Marian-Iancu-McLerran-Weigert-Leonidov-Kovner rapidity evolution equations and the amplitude of ∼cos2ϕ azimuthal asymmetries in deep inelastic scattering dijet production at high energies is estimated.
Abstract: We determine the distribution of linearly polarized gluons of a dense target at small x by solving the Balitsky-Jalilian-Marian-Iancu-McLerran-Weigert-Leonidov-Kovner rapidity evolution equations. From these solutions, we estimate the amplitude of ∼cos2ϕ azimuthal asymmetries in deep inelastic scattering dijet production at high energies. We find sizable long-range in rapidity azimuthal asymmetries with a magnitude in the range of v_{2}=⟨cos2ϕ⟩∼10%.
93 citations
TL;DR: In this article, the authors present an analytic analysis of the initial space-time evolution of the gluon field in the limit of very high energies using a formal recursive solution of the Yang-Mills equations.
Abstract: Nuclei colliding at very high energy create a strong, quasi-classical gluon field during the initial phase of their interaction. We present an analytic calculation of the initial space-time evolution of this field in the limit of very high energies using a formal recursive solution of the Yang-Mills equations. We provide analytic expressions for the initial chromo-electric and chromo-magnetic fields and for their energy-momentum tensor. In particular, we discuss event-averaged results for energy density and energy flow as well as for longitudinal and transverse pressure of this system. Our results are generally applicable if τ 1 / Q s . The transverse energy flow of the gluon field exhibits hydrodynamic-like contributions that follow transverse gradients of the energy density. In addition, a rapidity-odd energy flow also emerges from the non-abelian analog of Gauss' Law and generates non-vanishing angular momentum of the field. We will discuss the space-time picture that emerges from our analysis and its implications for observables in heavy ion collisions.
62 citations
TL;DR: In this article, it was shown that Bose enhancement in a hadronic wave function generically leads to correlations between produced particles, the so-called ridge correlations, which can be used to predict the long range rapidity correlations of the produced particles.
58 citations
TL;DR: In this paper, the origins of azimuthal correlations observed in high energy proton-nucleus collisions were examined by considering the simple example of the scattering of uncorrelated partons off color fields in a large nucleus.
Abstract: We examine the origins of azimuthal correlations observed in high energy proton-nucleus collisions by considering the simple example of the scattering of uncorrelated partons off color fields in a large nucleus. We demonstrate how the physics of fluctuating color fields in the color glass condensate (CGC) effective theory generates these azimuthal multiparticle correlations and compute the corresponding Fourier coefficients v_n within different CGC approximation schemes. We discuss in detail the qualitative and quantitative differences between the different schemes. We will show how a recently introduced color field domain model that captures key features of the observed azimuthal correlations can be understood in the CGC effective theory as a model of non-Gaussian correlations in the target nucleus.
47 citations
TL;DR: In this paper, a semi-holographic model for the out-of-equilibrium dynamics during the partonic stages of an ultrarelativistic heavy-ion collision was developed.
Abstract: We develop a semi-holographic model for the out-of-equilibrium dynamics during the partonic stages of an ultrarelativistic heavy-ion collision. The model combines a weakly-coupled hard sector, involving gluon modes with energy and momenta of the order of the saturation momentum and relatively large occupation numbers, with a strongly-coupled soft sector, which physically represents the soft gluons radiated by the hard partons. The hard sector is described by perturbative QCD, more precisely, by its semi-classical approximation (the classical Yang-Mills equations) which becomes appropriate when the occupation numbers are large. The soft sector is described by a marginally deformed conformal field theory, which in turn admits a holographic description in terms of classical Einstein’s equations in AdS
5 with a minimally coupled massless ‘dilaton’. The model involve two free parameters which characterize the gauge-invariant couplings between the hard and soft sectors. Via these couplings, the hard modes provide dynamical sources for the gravitational equations at the boundary of AdS
5 and feel the feedback of the latter as additional soft sources in the classical Yang-Mills equations. Importantly, the initial conditions for this coupled dynamics are fully determined by the hard sector alone, i.e. by perturbative QCD, and are conveniently given by the color glass condensate (CGC) effective theory. We also develop a new semi-holographic picture of jets in the QGP by attaching a non-Abelian charge to the endpoint of the trailing string in AdS
5 representing a heavy quark. This leads to modified Nambu-Goto equations for the string which govern the (collisional and radiative) energy loss by the heavy quark towards both hard and soft modes.
43 citations
TL;DR: In this article, the entanglement entropy of soft gluons in the wave function of a fast moving hadron and its basic properties were discussed and the expression for entropy production in a high energy hadronic collision within the color glass formalism was derived.
Abstract: We compute the entanglement entropy of soft gluons in the wave function of a fast moving hadron and discuss its basic properties. We also derive the expression for entropy production in a high energy hadronic collision within the color glass formalism. We show that long range rapidity correlations give negative contribution to the production entropy. We calculate the (naturally defined) temperature of the produced system of particles, and show that it is proportional to the average transverse momentum of the produced particles. Our calculations apply to the situation when at least one of the colliding objects is dilute.
39 citations
DSM1
TL;DR: In this article, the early stages of heavy ion collisions at high energy in the Color Glass Condensate framework are described, from the pre-collision high energy nuclear wave function to the point where hydrodynamics may start becoming applicable.
Abstract: In this review, I present the description of the early stages of heavy ion collisions at high energy in the Color Glass Condensate framework, from the pre-collision high energy nuclear wave function to the point where hydrodynamics may start becoming applicable.
33 citations
TL;DR: In this article, a study of the average transverse momentum (p T ) as a function of the mid-rapidity charged hadron multiplicity (N ch ) and hadron mass (m ) in p-Pb and pb-pb collisions at RHIC and LHC energies is presented.
19 citations
TL;DR: In this paper, the authors investigated the low transverse momentum heavy quarkonium collisions in the forward rapidity region of $pp$ and $pA$ collisions at the LHC as an important probe to the transverse velocity tomography of the gluons in hadrons in the color glass condensate (CGC) framework.
Abstract: We investigate the low transverse momentum heavy quarkonium ($J/\ensuremath{\psi}$, $\mathrm{\ensuremath{\Upsilon}}$) productions in the forward rapidity region of $pp$ and $pA$ collisions at the LHC as an important probe to the transverse momentum tomography of the gluons in hadrons in the color glass condensate (CGC) framework. By implementing the Sudakov resummation consistently in the CGC formalism, we achieve an excellent agreement between the improved CGC calculations and the LHC data. We show that both the small-$x$ and the Sudakov effects are essential for a complete description of heavy quarkonium productions in the low transverse momentum region. This provides a solid foundation to study the small-$x$ gluon saturation in a big nucleus with the future $pA$ programs at the LHC.
17 citations
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TL;DR: In this paper, a semi-holographic model for heavy-ion collisions is proposed, which includes self-consistent couplings between the Yang-Mills fields of the Color Glass Condensate framework and an infrared AdS/CFT sector, such as to guarantee the existence of a conserved energy-momentum tensor for the combined system.
Abstract: We present an extended version of a recently proposed semi-holographic model for heavy-ion collisions, which includes self-consistent couplings between the Yang-Mills fields of the Color Glass Condensate framework and an infrared AdS/CFT sector, such as to guarantee the existence of a conserved energy-momentum tensor for the combined system that is local in space and time, which we also construct explicitly. Moreover, we include a coupling of the topological charge density in the glasma to the same of the holographic infrared CFT. The semi-holographic approach makes it possible to combine CGC initial conditions and weak-coupling glasma field equations with a simultaneous evolution of a strongly coupled infrared sector describing the soft gluons radiated by hard partons. As a first numerical test of the semi-holographic model we study the dynamics of fluctuating homogeneous color-spin-locked Yang-Mills fields when coupled to a homogeneous and isotropic energy-momentum tensor of the holographic IR-CFT, and we find rapid convergence of the iterative numerical procedure suggested earlier.
TL;DR: In this paper, the authors proposed a solution to the long-standing problem of the color glass condensate (CGC)/saturation approach: the powerlike fall of the scattering amplitudes at large $b$.
Abstract: In this paper we proposed a solution to the long-standing problem of the color glass condensate(CGC)/saturation approach: the powerlike fall of the scattering amplitudes at large $b$. This decrease leads to the violation of the Froissart theorem and makes the approach theoretically inconsistent. We showed in the paper that the sum of the pion loops results in the exponential fall of the scattering amplitude at large impact parameters and in the restoration of the Froissart theorem.
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TL;DR: In this paper, it was shown that Bose enhancement in a hadronic wave function generically leads to correlations between produced particles, the so-called ridge correlations, which can be used to predict the long range rapidity correlations of the produced particles.
Abstract: We point out that Bose enhancement in a hadronic wave function generically leads to correlations between produced particles. We show explicitly, by calculating the projectile density matrix in the Color Glass Condensate approach to high-energy hadronic collisions, that the Bose enhancement of gluons in the projectile leads to azimuthal collimation of long range rapidity correlations of the produced particles, the so-called ridge correlations.
TL;DR: In this paper, the authors extend these previous findings to the case of experimental data on elliptic flow and find an excellent scaling for all centralities and energies, from RHIC to LHC, with a simple generalization of the scaling previously found for other observables and systems.
Abstract: The presence of scaling variables in experimental observables provide very valuable indications of the dynamics underlying a given physical process. In the last years, the search for geometric scaling, that is the presence of a scaling variable which encodes all geometrical information of the collision as well as other external quantities as the total energy, has been very active. This is motivated, in part, for being one of the genuine predictions of the Color Glass Condensate formalism for saturation of partonic densities. Here we extend these previous findings to the case of experimental data on elliptic flow. We find an excellent scaling for all centralities and energies, from RHIC to LHC, with a simple generalization of the scaling previously found for other observables and systems. Interestingly the case of the photons, difficult to reconcile in most formalisms, nicely fit the scaling curve. We discuss the possible interpretations of this finding in terms of initial or final state effects.
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TL;DR: In this paper, the authors argue that large fluctuations in the saturation momentum are necessary to explain the ATLAS and ALICE data on pA collisions measured at the LHC and use a form for the distribution of fluctuations motivated by theoretical studies of the nonlinear evolution equations for the Color Glass Condensate.
Abstract: We argue that large fluctuations in the saturation momentum are necessary to explain the ATLAS and ALICE data on pA collisions measured at the LHC. Using a form for the distribution of fluctuations motivated by theoretical studies of the non-linear evolution equations for the Color Glass Condensate, we find a remarkably good agreement between theory and the measured distributions. If the saturation momentum fluctuates, we argue that the cross section for a proton probe should also fluctuate, consistent with previous observations. Finally we discuss these results and their possible consistency with what is known about multiplicity fluctuations in such collisions, and attempts to describe the ridge effect from properties of the initial state.
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TL;DR: In this paper, the authors re-evaluate the nuclear suppression of forward $J/psi$ production at high energy in the Color Glass Condensate framework and show that using the Glauber approach to generalize the proton dipole cross section to the case of a nucleus target leads to a nuclear modification factor much closer to LHC data than previous estimates using the same framework.
Abstract: We re-evaluate the nuclear suppression of forward $J/\psi$ production at high energy in the Color Glass Condensate framework. We use the collinear approximation for the projectile proton probed at large $x$ and an up to date dipole cross section fitted to HERA data to describe the target in proton-proton collisions. We show that using the Glauber approach to generalize the proton dipole cross section to the case of a nucleus target leads to a nuclear modification factor much closer to LHC data than previous estimates using the same framework.
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TL;DR: In this article, the authors argue that large fluctuations in the saturation momentum are necessary to explain the ATLAS and ALICE data on pA collisions measured at the LHC and use a form for the distribution of fluctuations motivated by theoretical studies of the nonlinear evolution equations for the Color Glass Condensate.
Abstract: We argue that large fluctuations in the saturation momentum are necessary to explain the ATLAS and ALICE data on pA collisions measured at the LHC. Using a form for the distribution of fluctuations motivated by theoretical studies of the non-linear evolution equations for the Color Glass Condensate, we find a remarkably good agreement between theory and the measured distributions. If the saturation momentum fluctuates, we argue that the cross section for a proton probe should also fluctuate, consistent with previous observations. Finally we discuss these results and their possible consistency with what is known about multiplicity fluctuations in such collisions, and attempts to describe the ridge effect from properties of the initial state.
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TL;DR: In this article, the PHENIX results for d+Au and $3He$ +Au collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) are presented.
Abstract: Features of collectivity observed in high energy A+A collision systems at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) imply a strongly coupled quark gluon plasma (QGP) that flows. One defining feature of collectivity is long-range angular correlations which are characterized experimentally by measuring the azimuthal anisotropy of particles well separated in rapidity. Evidence indicating long-range angular correlations include the appearance of the so-called near-side "ridge" in correlation functions and $p_T$ dependent flow components ($v_N$). These features have been well measured at RHIC for Au+Au collisions at $\sqrt{s_{NN}} $= 200 GeV and at the LHC for Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. However, evidence of collectivity has recently been observed at the LHC in p+p high multiplicity collisions at $\sqrt{s_{NN}}$ = 7.0 TeV and p+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV and then at RHIC in d+Au and $3^He$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. In this talk, we present the recent PHENIX results for d+Au and $^3He$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Precise measurements of anisotropy help distinguish between theoretical models based on relativistic hydrodynamics or Color Glass Condensate (CGC). Comparisons of these measurements to various theoretical models are shown.
TL;DR: In this article, the authors extend these previous findings to the case of experimental data on elliptic flow and find an excellent scaling for all centralities and energies, from RHIC to LHC, with a simple generalization of the scaling previously found for other observables and systems.
Abstract: The presence of scaling variables in experimental observables provide very valuable indications of the dynamics underlying a given physical process. In the last years, the search for geometric scaling, that is the presence of a scaling variable which encodes all geometrical information of the collision as well as other external quantities as the total energy, has been very active. This is motivated, in part, for being one of the genuine predictions of the Color Glass Condensate formalism for saturation of partonic densities. Here we extend these previous findings to the case of experimental data on elliptic flow. We find an excellent scaling for all centralities and energies, from RHIC to LHC, with a simple generalization of the scaling previously found for other observables and systems. Interestingly, the case of the photons, di cult to reconcile in most formalisms, nicely fit the scaling curve. We discuss on the possible interpretations of this finding in terms of initial or final state e ects.
DSM1
TL;DR: In this paper, the early stages of heavy ion collisions at high energy in the Color Glass Condensate framework are described, from the pre-collision high energy nuclear wavefunction to the point where hydrodynamics may start becoming applicable.
Abstract: In this review, I present the description of the early stages of heavy ion collisions at high energy in the Color Glass Condensate framework, from the pre-collision high energy nuclear wavefunction to the point where hydrodynamics may start becoming applicable.
TL;DR: In this paper, the two-and multi-particle correlations in pPb collisions from the LHC were analyzed over a wide event multiplicity and transverse momentum range.
Abstract: We develop a Monte Carlo event generator based on the combination of a parton production formula including the effects of parton saturation (called the DHJ formula) and a hadronization process due to the Lund string fragmentation model. This event generator is designed for the description of hadron productions at forward rapidities and in a wide transverse momentum range in high-energy proton-proton collisions. We analyze transverse momentum spectra of charged hadrons as well as identified particles, including pion, kaon, and (anti) proton at RHIC energy and ultraforward neutral pion spectra from the LHCf experiment. We compare our results to those obtained in other models based on parton-hadron duality and fragmentation functions.
TL;DR: In this article, the color glass condensate formalism was used to study the pT spectra in p+p and p+Pb collisions by considering an energy-dependent broadening of nucleon density distribution.
Abstract: In the Color Glass Condensate formalism, charged hadron pT spectra in p+p and p+Pb collisions are studied by considering an energy-dependent broadening of nucleon density distribution. Then, in the glasma flux tube picture, the n-particle multiplicity distributions at different pseudo-rapidity ranges are investigated. Both the theoretical results show good agreement with the recent experimental data from ALICE and CMS at LHC energies. The predictive results for pT or multiplicity distributions in p+p and p+Pb collisions at the Large Hadron Collider are also given in this paper.
24 Jun 2015
TL;DR: In this article, the color glass condensate (CGC) framework is applied to various scattering processes, such as electron-proton deep inelastic scattering (DIS), protonproton and proton-nucleus collisions.
Abstract: In this thesis the Color Glass Condensate (CGC) framework, which describes quantum chromodynamics (QCD) at high energy, is applied to various scattering processes. Higher order corrections to the CGC evolution equations, known as the BK and JIMWLK equations, are also considered. It is shown that the leading order CGC calculations describe the experimental data from electron-proton deep inelastic scattering (DIS), proton-proton and proton-nucleus collisions. The initial condition for the BK evolution equation is obtained by performing a fit to deep inelastic scattering data. The fit result is used as an input to calculations of single particle spectra and nuclear suppression in proton-proton and proton-nucleus collisions, which are shown to be in agreement with RHIC and LHC measurements. In particular, the importance of a proper description of the nuclear geometry consistently with the DIS data fits is emphasized, as it results in a nuclear suppression factor $R_{pA}$ which is consistent with the available experimental data. In addition to single particle production, the correlations between two hadrons at forward rapidity are computed. The RHIC measurements are shown to be naturally explainable in the CGC framework, and the previous CGC calculations are improved by including the so called inelastic and double parton scattering contributions. This improvement is shown to be required in order to get results compatible with the experimentally measured correlations. Exclusive vector meson production, which can be a powerful tool to study the gluonic structure of nuclei at small Bjorken-$x$, is also considered. The cross sections are calculated within the CGC framework in the context of a future electron-ion collider. In particular, the cross section for incoherent diffractive vector meson production is derived and a centrality estimator for this process is proposed.
TL;DR: In this article, the authors derived the production rate for the light vector mesons produced by gluon-gluon fusion in the kT-factorization approach, and the numerical results indicate that the mesons from the color glass condensate become prominent in p-p, p-Pb, and Pb-pb collisions at Large Hadron Collider (LHC) energies.
Abstract: We calculate inclusive light vector mesons (ρ, ω, and ) production in relativistic heavy ion collisions based on the idea of gluon saturation in the color glass condensate (CGC) framework. At high energies, the value of saturation momentum becomes larger than the Quantum Chromodynamics (QCD) confinement scale ΛQCD, which implies that αs(Qs) 1. Using the relativistic kinetic theory, we derive the production rate for the light vector mesons produced by gluon-gluon fusion in the kT-factorization approach. The numerical results indicate that the light vector mesons from the color glass condensate become prominent in p-p, p-Pb, and Pb-Pb collisions at Large Hadron Collider (LHC) energies.
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TL;DR: In this paper, the color glass condensate (CGC) framework is applied to various scattering processes, such as electron-proton deep inelastic scattering (DIS), protonproton and proton-nucleus collisions, and correlations between two hadrons at forward rapidity are computed.
Abstract: In this thesis the Color Glass Condensate (CGC) framework, which describes quantum chromodynamics (QCD) at high energy, is applied to various scattering processes. Higher order corrections to the CGC evolution equations, known as the BK and JIMWLK equations, are also considered.
It is shown that the leading order CGC calculations describe the experimental data from electron-proton deep inelastic scattering (DIS), proton-proton and proton-nucleus collisions. The initial condition for the BK evolution equation is obtained by performing a fit to deep inelastic scattering data. The fit result is used as an input to calculations of single particle spectra and nuclear suppression in proton-proton and proton-nucleus collisions, which are shown to be in agreement with RHIC and LHC measurements. In particular, the importance of a proper description of the nuclear geometry consistently with the DIS data fits is emphasized, as it results in a nuclear suppression factor $R_{pA}$ which is consistent with the available experimental data.
In addition to single particle production, the correlations between two hadrons at forward rapidity are computed. The RHIC measurements are shown to be naturally explainable in the CGC framework, and the previous CGC calculations are improved by including the so called inelastic and double parton scattering contributions. This improvement is shown to be required in order to get results compatible with the experimentally measured correlations.
Exclusive vector meson production, which can be a powerful tool to study the gluonic structure of nuclei at small Bjorken-$x$, is also considered. The cross sections are calculated within the CGC framework in the context of a future electron-ion collider. In particular, the cross section for incoherent diffractive vector meson production is derived and a centrality estimator for this process is proposed.
TL;DR: In this paper, the early stages of a heavy-ion collision at high energy in the colour glass condensate (CGC) framework are described, and a short review is presented.
Abstract: In this short review, we present the description of the early stages of a heavy-ion collision at high energy in the colour glass condensate (CGC) framework.
TL;DR: In this article, the color glass condensate formalism was used to study the particle multiplicity distributions at different pseudo-rapidity ranges in the Large Hadron Collider (LHC).
Abstract: In the Color Glass Condensate formalism, charged hadron p_{T} distributions in p+p collisions are studied by considering an energy-dependent broadening of nucleon's density distribution. Then, in the Glasma flux tube picture, the n-particle multiplicity distributions at different pseudo-rapidity ranges are investigated. Both of the theoretical results show good agreement with the recent experimental data from ALICE and CMS at \sqrt{s}=0.9, 2.36, 7 TeV. The predictive results for p_{T} and multiplicity distributions in p+p and p+Pb collisions at the Large Hadron Collider are also given in this paper.
19 May 2015
TL;DR: In this article, the transition from the Lorentz contracted sheets of hadrons, the color glass condensate, to thermal QCD matter is the core of this work, which involves to further develop both the theoretical foundations of the description of initial state fluctuations and the computational framework for the turbulent dynamics of nuclear matter at extreme energy densities.
Abstract: The standard model of relativistic heavy-ion collisions describes the hadronic collision in four distinct stages: the initial Color glass condensate, the glasma, the quark gluon plasma and finally the hot hadron gas. Exploring the transition from at first Lorentz contracted sheets of hadrons, the color glass condensate, to thermal QCD matter is the core of this work. The study of anisotropically expanding plasmas shows that non-Abelian plasmas isotropize fast enough thanks to the chromo-Weibel instability. In recent work we find filamentation instabilities in SU(3) Yang-Mills plasma. Real time simulations are a highly promising approach to shed light on the fast thermalization of non-equilibrium matter. This involves to further develop both the theoretical foundations of the description of initial-state fluctuations and the computational framework for the turbulent dynamics of nuclear matter at extreme energy densities.