Showing papers on "Color-glass condensate published in 2005"

Evolution at small x_bj: The Color Glass Condensate

Abstract: When probed at very high energies or small Bjorken x_bj, QCD degrees of freedom manifest themselves as a medium of dense gluon matter called the Color Glass Condensate. Its key property is the presence of a density induced correlation length or inverse saturation scale R_s=1/Q_s. Energy dependence of observables in this regime is calculable through evolution equations, the JIMWLK equations, and characterized by scaling behavior in terms of Q_s. These evolution equations share strong parallels with specific counterparts in jet physics. Experimental relevance ranges from lepton proton and lepton nucleus collisions to heavy ion collisions and cross correlates physics at virtually all modern collider experiments.

Breakdown of QCD factorization at large Feynman x

Abstract: Recent measurements by the BRAHMS Collaboration of high-p{sub T} hadron production at forward rapidities at the BNL Relativistic Heavy Ion Collider found the relative production rate (d-Au)/(p-p) to be suppressed rather than enhanced. Examining other known reactions (forward production of light hadrons, the Drell-Yan process, heavy flavor production, etc.), one notes that all of these display a similar property, namely, their cross sections in nuclei are suppressed at large x{sub F}. Since this is the region where x{sub 2} is minimal, it is tempting to interpret this as a manifestation of coherence or of a color glass condensate, whereas it is actually a simple consequence of energy conservation and takes place even at low energies. We demonstrate that in all these reactions there is a common suppression mechanism that can be viewed, alternatively, as a consequence of a reduced survival probability for large rapidity gap processes in nuclei, a Sudakov suppression, an enhanced resolution of higher Fock states by nuclei, or an effective energy loss that rises linearly with energy. Our calculations agree with the data.

Classical odderon in QCD at high energies

Abstract: We show that the weight functional for color sources in the classical theory of the color glass condensate (CGC) includes a term which generates odderon excitations Remarkably, the classical origin of these excitations can be traced to the random walk of partons in the two dimensional space spanned by the SU(3) Casimirs We compute dipole and baryon odderon operators in the CGC and show that contributions from the classical color sources to these are suppressed in the limit of very large parton densities

Quantitative study of the violation of k⊥ factorization in hadroproduction of quarks at collider energies

Abstract: We demonstrate the violation of kperpendicular factorization for quark production in high energy hadronic collisions. This violation is quantified in the color glass condensate framework and studied as a function of the quark mass, the quark transverse momentum, and the saturation scale Q(s), which is a measure of large parton densities. At x values where parton densities are large but leading twist shadowing effects are still small, violations of kperpendicularkfactorization can be significant--especially for lighter quarks. At very small x, where leading twist shadowing is large, we show that violations of kperpendicular factorization are relatively weaker.

Forward Production in d+Au Collisions by Parton Recombination

Abstract: We discuss parton recombination as a hadronization mechanism for d+Au collisions. We show that several features of hadron production measured at the Relativistic Heavy Ion Collider (RHIC) can be explained by recombination, including the Cronin effect at midrapidity and the suppression of hadrons in forward direction.

A Weibel Instability in the Melting Color Glass Condensate

Abstract: Based on 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 $\exp{(\Gamma \sqrt{g^2\mu \tau})}$ (where $g^2\mu$ is a scale arising from the saturation of gluons in the nuclear wavefunction) 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 find good agreement when we relate $\Gamma$ to the prediction from kinetic theory.

Quark production in high-energy proton-nucleus collisions

Abstract: In this note, we discuss the problem of quark-antiquark pair production in the framework of the color glass condensate. The cross-section can be calculated in closed form for the case of proton-nucleus collisions, where the proton can be considered to be a dilute object. We find that $k_\perp$ -factorization is broken by rescattering effects.

CGC, QCD saturation and RHIC data (Kharzeev-Levin-McLerran-Nardi point of view)

Abstract: We are going to discuss ion-ion and deuteron-nucleus RHIC data and show that they support, if not more, the idea of the new QCD phase: Colour Glass Condensate with saturated parton density.

Dense gluon matter in nuclear collisions

Abstract: Theoretical and phenomenological aspects of the physics of high-energy heavy-ion collisions are reviewed with emphasis on ideas related to the theory and phenomenology of color glass condensate.

Hydrodynamic afterburner for the colour glass condensate at RHIC

Abstract: Firstly, we give a short review of the hydrodynamic model and its application to the elliptic flow phenomena in relativistic heavy-ion collisions. Secondly, we describe the first attempt to construct a unified model for the description of the dynamics in relativistic heavy-ion collisions.

Testing universality of the color glass condensate descriptions

Abstract: Perturbative quantum chromodynamics predicts that the small-x gluons in a hadron wavefunction should form a color glass condensate (CGC), which has universal properties, which are the same for all hadrons or nuclei. Assuming this property, in this paper we cross-relate the current CGC descriptions of the ep HERA data and dAu RHIC data. In particular, we use the quark dipole scattering amplitude recently proposed by Kharzeev, Kovchegov and Tuchin (KKT) to explain the high pT particle suppression observed in dAu collisions at RHIC in our calculations of the proton and longitudinal structure functions. We present a detailed comparison between this parameterization and those proposed to describe the ep HERA data. We find that, due to its peculiar dependence on the energy and dipole separation, the KKT parameterization is able to describe the experimental ep data only in a limited kinematical range of photon virtualities.

Hunting the quark gluon plasma

Abstract: The U.S. Department of Energy's Relativistic Heavy Ion Collider (RHIC) construction project was completed at BNL in 1999, with the first data-taking runs in the summer of 2000. Since then the early measurements at RHIC have yielded a wealth of data, from four independent detectors, each with its international collaboration of scientists: BRAHMS, PHENIX, PHOBOS, and STAR [1]. For the first time, collisions of heavy nuclei have been carried out at colliding-beam energies that have previously been accessible only for high-energy physics experiments with collisions of ''elementary'' particles such as protons and electrons. It is at these high energies that the predictions of quantum chromodynamics (QCD), the fundamental theory that describes the role of quarks and gluons in nuclear matter, come into play, and new phenomena are sought that may illuminate our view of the basic structure of matter on the sub-atomic scale, with important implications for the origins of matter on the cosmic scale. The RHIC experiments have recorded data from collisions of gold nuclei at the highest energies ever achieved in man-made particle accelerators. These collisions, of which hundreds of millions have now been examined, result in final states of unprecedented complexity, with thousands of produced particles radiatingmore » from the nuclear collision. All four of the RHIC experiments have moved quickly to analyze these data, and have begun to understand the phenomena that unfold from the moment of collision as these particles are produced. In order to provide benchmarks of simpler interactions against which to compare the gold-gold collisions, the experiments have gathered comparable samples of data from collisions of a very light nucleus (deuterium) with gold nuclei, as well as proton-proton collisions, all with identical beam energies and experimental apparatus. The early measurements have revealed compelling evidence for the existence of a new form of nuclear matter at extremely high density and temperature--a medium in which the predictions of QCD can be tested, and new phenomena explored, under conditions where the relevant degrees of freedom, over nuclear volumes, are expected to be those of quarks and gluons, rather than of hadrons. This is the realm of the quark gluon plasma, the predicted state of matter whose existence and properties are now being explored by the RHIC experiments.« less

Expression of interest for a comprehensive new detector at RHIC II

Abstract: There are compelling physics questions to be addressed by a new comprehensive detector at a future, high-luminosity RHIC II collider. These form the basis for this Expression of Interest. What precisely are the properties of the strongly-coupled Quark Gluon Plasma (sQGP)? Can a more weakly interacting QGP state be formed and investigated at RHIC? How do particles acquire mass and what is the effect of chiral symmetry restoration on hadronization in a dense medium? What is the chiral structure of the QCD vacuum and its influence on and contributions of different QCD vacuum states to the masses of particles? Is there another phase of matter at low Bjorken-x, i.e. the Color Glass Condensate (CGC)? If present, what are its features and how does it evolve into the QGP? If not, are parton distribution functions understood at low Bjorken-x and can they describe particle production? What are the structure and dynamics inside the proton, including parton spin and orbital angular momentum? What are the contributions of gluons and the QCD sea to the polarization of the proton? What is the flavor-dependence? Are there tests for new physics beyond the Standard Model from spin measurements at RHIC II (such as parity-violating interactions)? We propose that a new comprehensive detector system is needed for RHIC II to address these questions adequately and in an effective way.

Open and hidden charm production in pA collisions

Abstract: We discuss the production of charmed mesons and \(J/\Psi\) in p(d)A collisions at high energies. We argue that when the saturation scale Qs characterizing the parton density in a nucleus exceeds the quark mass m, the naive perturbation theory breaks down. Consequently, we calculate the process of heavy quark production in both open and hidden channels in the framework of the parton saturation model (color glass condensate). We demonstrate that at RHIC such a description is in agreement with experimental data on charm production.