Showing papers on "Color-glass condensate published in 2011"

Gluons and the Quark Sea at High Energies: Distributions, Polarization, Tomography

Abstract: This report is based on a ten-week program on "Gluons and the quark sea at high-energies", which took place at the Institute for Nuclear Theory in Seattle in Fall 2010. The principal aim of the program was to develop and sharpen the science case for an Electron-Ion Collider (EIC), a facility that will be able to collide electrons and positrons with polarized protons and with light to heavy nuclei at high energies, offering unprecedented possibilities for in-depth studies of quantum chromodynamics. This report is organized around four major themes: i) the spin and flavor structure of the proton, ii) three-dimensional structure of nucleons and nuclei in momentum and configuration space, iii) QCD matter in nuclei, and iv) Electroweak physics and the search for physics beyond the Standard Model. Beginning with an executive summary, the report contains tables of key measurements, chapter overviews for each of the major scientific themes, and detailed individual contributions on various aspects of the scientific opportunities presented by an EIC.

Distribution of linearly polarized gluons inside a large nucleus

Abstract: The distribution of linearly polarized gluons inside a large nucleus is studied in the framework of the color glass condensate. We find that the Weizsacker-Williams distribution saturates the positivity bound at large transverse momenta and is suppressed at small transverse momenta, whereas the dipole distribution saturates the bound for any value of the transverse momentum. We also discuss processes in which both distributions of linearly polarized gluons can be probed.

Elliptic flow: a brief review

Abstract: One of the fundamental questions in the field of subatomic physics is the question of what happens to matter at extreme densities and temperatures as may have existed in the first microseconds after the Big Bang and exists, perhaps, in the core of dense neutron stars. The aim of heavy-ion physics is to collide nuclei at very high energies and thereby create such a state of matter in the laboratory. The experimental program began in the 1990s with collisions made available at the Brookhaven Alternating Gradient Synchrotron (AGS) and the CERN Super Proton Synchrotron (SPS), and continued at the Brookhaven Relativistic Heavy-Ion Collider (RHIC) with the maximum center- of-mass energies of p sNN = 4.75, 17.2 and 200GeV, respectively. Collisions of heavy ions at the unprecedented energy of 2.76TeV recently became available at the LHC collider at CERN. In this review, I give a brief introduction to the physics of ultrarelativistic heavy-ion collisions and discuss the current status of elliptic flow measurements. Contents

k(t) factorization for hard processes in nuclei.

Abstract: Two widely proposed kt-dependent gluon distributions in the small-x saturation regime are investigated using two particle back-to-back correlations in high energy scattering processes. The Weizsacker-Williams gluon distribution, interpreted as the number density of gluon inside the nucleus, is studied in the quark-antiquark jet correlation in deep inelastic scattering. On the other hand, the unintegrated gluon distribution, defined as the Fourier transform of the color-dipole cross section, is probed in the direct photon-jet correlation in pA collisions. Dijet-correlation in pA collisions depends on both gluon distributions through combination and convolution in the large Nc limit. We calculate these processes in two approaches: the transverse momentum dependent factorization approach and the color-dipole/color glass condensate formalism, and they agree with each other completely.

kt-factorization for Hard Processes in Nuclei

Abstract: Two widely proposed kt-dependent gluon distributions in the small-x saturation regime are investigated using two particle back-to-back correlations in high energy scattering processes. The Weizsacker-Williams gluon distribution, interpreted as the number density of gluon inside the nucleus, is studied in the quark-antiquark jet correlation in deep inelastic scattering. On the other hand, the unintegrated gluon distribution, defined as the Fourier transform of the color-dipole cross section, is probed in the direct photon-jet correlation in pA collisions. Dijet-correlation in pA collisions depends on both gluon distributions through combination and convolution in the large Nc limit. We calculate these processes in two approaches: the transverse momentum dependent factorization approach and the color-dipole/color glass condensate formalism, and they agree with each other completely.

Vector meson production in coherent hadronic interactions: Update on predictions for energies available at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider

Abstract: In this Rapid Communication we update our predictions for the photoproduction of vector mesons in coherent $\mathit{pp}$ and $\mathit{AA}$ collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies using the color dipole approach and the Color Glass Condensate formalism. In particular, we present our predictions for the first run of the LHC at half energy and for the rapidity dependence of the ratio between the $J/\ensuremath{\Psi}$ and $\ensuremath{\rho}$ cross sections at RHIC energies.

SMALL x PHYSICS AND RHIC DATA

Abstract: This is a review of applications of the Color Glass Condensate (CGC) to the phenomenology of relativistic heavy-ion collisions. The initial stages of the collision can be understood in terms of the nonperturbatively strong nonlinear glasma color fields. We discuss how the CGC framework can and has been used to compute properties of the initial conditions of AA collisions. In particular this has led to recent progress in understanding multiparticle correlations, which can provide a directly observable signal of the properties of the initial stage of the collision process.

Two-particle azimuthal correlations at forward rapidity in STAR

Abstract: During the 2008 run the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven Nation Laboratiory (BNL), NY, provided high luminosity in both p+p and d+Au collisions at $\sqrt{s_{NN}}=200\mathrm{\,GeV}$. Electromagnetic calorimeter acceptance in STAR was enhanced by the new Forward Meson Spectrometer (FMS), and is now almost contiguous from $-1

Extracting the Distribution Amplitudes of the ρ meson from the Color Glass Condensate

Abstract: We extract the twist-2 and twist-3 Distribution Amplitudes (DAs) of the ρ meson using the HERA data on diffractive ρ photoproduction. We do so using several Colour Glass Condensate (CGC) inspired and a Regge inspired dipole models. We find that our extracted twist-2 DA is not much model dependent and is consistent with QCD Sum Rules and lattice predictions. The extracted twist-3 DA is more model dependent but is still consistent with the Sum Rules prediction.

CGC initial conditions at RHIC and LHC

Abstract: Monte-Carlo implementations of kT-factorization formula with both KLN and running-coupling BK unintegrated gluon distributions for nucleus-nucleus collisions are used to analyze recent experimental data on the particle multiplicities from RHIC(Au+Au@200GeV) and LHC(Pb+Pb@2.76TeV). We also compare the predicted transverse energy at midrapidity to new data from ALICE.

The CGC and the Glasma: Two lectures at the Yukawa Institute

Abstract: These lectures present the theory of the Color Glass Condensate (CGC) and the Glasma in an elementary and intuitive manner. This matter controls the high energy limit of QCD. The CGC is the universal limit for the components of a hadron wavefunction important for high energy scattering processes. It is a highly coherent, extremely high energy density ensemble of gluon states. The Glasma is matter produced in the collision of CGCs of two hadrons. It has properties much different from those of the CGC, and is produced in a very short time after the collision. It eventually evolves from the the Color Glass Condensate initial conditions into a Quark Gluon Plasma. We can visualize the collision of two high energy hadrons as shown in Fig. 1. Before the collision, two hadrons appear as Lorentz contracted sheets approaching one another at near light speed. These we will later describe as two sheets of Colored Glass. In a very short time, the sheets of Color Glass interpenetrate one another. This we think of as the initial singularity for the collision. This is of course not a real singularity for finite collision energy, but we will see it becomes one in the limitmore » of infinite energy. After the initial singularity, a Glasma is formed. This is composed of highly coherent gluon fields of very high energy density. If we imagine that the sheets of Colored Glass have passed through one another largely intact, the Glasma forms in the region between the receding sheets. As time goes on, the Glasma evolves into a Quark Gluon Plasma, and eventually into a gas of ordinary hadrons. These lectures are about the earliest stages of these collisions, and will describe neither the Quark Gluon Plasma nor the Hadron Gas. I will motivate the CGC and Glasma from simple physical considerations, and provide a sketchy derivation from QCD. There will be some discussion of experimental tests of these ideas.« less

Forward particle productions at the RHIC and the LHC from CGC within local rcBK evolution

Abstract: In order to describe forward hadron production in high-energy nuclear collisions, we propose a Monte Carlo implementation of the Dumitru–Hayashigaki–Jalilian-Marian formula with the unintegrated gluon distribution obtained numerically from the running-coupling BK equation. We discuss the influence of initial conditions for the BK equation by comparing a model constrained by a global fit of small-x HERA data and a newly proposed one from the 'running-coupling MV model'.

The early stages of a high energy heavy ion collision

Abstract: At high energy, the gluon distribution in nuclei reaches large densities and eventually saturates due to recombinations, that play an important role in heavy ion collisions at RHIC and the LHC. The Color Glass Condensate provides a framework for resumming these effects in the calculation of observables. In this talk, I present its application to the description of the early stages of heavy ion collisions.

Extracting the Distribution Amplitudes of the rho meson from the Color Glass Condensate

Abstract: We extract the leading twist-2 and subleading twist-3 Distribution Amplitudes (DAs) of the rho meson using the HERA data on diffractive rho photoproduction. We do so using several Colour Glass Condensate (CGC) inspired and a Regge inspired dipole models. We find that our extracted twist-2 DA is not much model dependent and is consistent with QCD Sum Rules and lattice predictions. The extracted twist-3 DA is more model dependent but is still consistent with the Sum Rules prediction.

Non-linear QCD dynamics in two-photon interactions at high energies

Abstract: Perturbative QCD predicts that the growth of the gluon density at high energies should saturate, forming a Color Glass Condensate (CGC), which is described in mean field approximation by the Balitsky–Kovchegov (BK) equation. In this paper we study the γγ interactions at high energies and estimate the main observables which will be probed at future linear colliders using the color dipole picture. We discuss in detail the dipole–dipole cross section and propose a new relation between this quantity and the dipole scattering amplitude. The total γγ, γ ∗ γ ∗ cross sections and the real photon structure function $F_{2}^{\gamma }(x,Q^{2})$ are calculated using the recent solution of the BK equation with running coupling constant and the predictions are compared with those obtained using phenomenological models for the dipole–dipole cross section and scattering amplitude. We demonstrate that these models are able to describe the LEP data at high energies, but predict a very different behavior for the observables at higher energies. Therefore we conclude that the study of γγ interactions can be useful to constrain the QCD dynamics.

Sensitivity of azimuthal jet tomography to early-time energy loss at RHIC and LHC

Abstract: We compute the path-length dependence of energy loss for higher azimuthal harmonics of jet fragments in a generalized model of energy loss that can interpolate between pQCD and AdS/CFT limits and compare results with Glauber and CGC/KLN initial conditions. We find, however, that even the high-pT second moment is most sensitive to the poorly known early-time evolution during the first fm/c. Moreover, we demonstrate that quite generally the energy and density dependence leads to an overquenching of high-pT particles relative to the first LHC RAA-data, once the parameters of the energy-loss model are fixed from RAA-data at RHIC.

CGC and initial state effects in Heavy Ion Collisions

Abstract: A brief review of the phenomenological studies in the field of heavy ion collisions based on the Color Glass Condensate theory and, in particular, of those relying in the use of the BK equation including running coupling effects is presented.

Quark gluon plasma, color glass condensate and glasma: 3 Lectures at Lake Baikal

Abstract: These lectures concern the properties of strongly interacting matter at very high energy density. I begin with the properties of the Quark Gluon Plasma and Quarkyonic Matter. I later discuss the Color Glass Condensate and the Glasma, matter that controls the earliest times in hadronic collisions. I then describe the Quark Gluon Plasma, matter produced from the thermalized remnants of the Glasma. The discussion will be intuitive and based on simple structural aspects of QCD. There will be some discussion of experimental tests of these ideas.