Showing papers on "Color-glass condensate published in 2013"

Comparison of the color glass condensate to dihadron correlations in proton-proton and proton-nucleus collisions

Abstract: We perform a detailed comparison of long-range rapidity correlations in the color glass condensate framework to high multiplicity dihadron data in proton-proton and proton-lead collisions from the CMS, ALICE and ATLAS experiments at the LHC. The overall good agreement thus far of the nontrivial systematics of theory with data is strongly suggestive of gluon saturation and the presence of subtle quantum interference effects between rapidity separated gluons. In particular, the yield of pairs collimated in their relative azimuthal angle $\ensuremath{\Delta}\ensuremath{\phi}\ensuremath{\sim}0$, is sensitive to the shape of unintegrated gluon distributions in the hadrons that are renormalization group evolved in rapidity from the beam rapidities to those of the measured hadrons. We present estimates for the collimated dihadron yield expected in central deuteron-gold collisions at the Relativistic Heavy Ion Collider.

Predictions for $p+$Pb Collisions at sqrt s_NN = 5 TeV

Abstract: Predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge bosons in p+Pb collisions at $\sqrt{s_{_{\it NN}}} = 5\, {\rm TeV}$ are compiled and compared. When test run data are available, they are compared to the model predictions.

Long-Range Rapidity Correlations in Heavy-Light Ion Collisions

Abstract: We study two-particle long-range rapidity correlations arising in the early stages of heavy ion collisions in the saturation/Color Glass Condensate framework, assuming for simplicity that one colliding nucleus is much larger than the other. We calculate the two-gluon production cross section while including all-order saturation effects in the heavy nucleus with the lowest-order rescattering in the lighter nucleus. We find four types of correlations in the two-gluon production cross section: (i) geometric correlations, (ii) HBT correlations accompanied by a back-to-back maximum, (iii) away-side correlations, and (iv) near-side azimuthal correlations which are long-range in rapidity. The geometric correlations (i) are due to the fact that nucleons are correlated by simply being confined within the same nucleus and may lead to long-range rapidity correlations for the produced particles without strong azimuthal angle dependence. Somewhat surprisingly, long-range rapidity correlations (iii) and (iv) have exactly the same amplitudes along with azimuthal and rapidity shapes: one centered around Δ ϕ = π with the other one centered around Δ ϕ = 0 (here Δϕ is the azimuthal angle between the two produced gluons). We thus observe that the early-time CGC dynamics in nucleus–nucleus collisions generates azimuthal non-flow correlations which are qualitatively different from jet correlations by being long-range in rapidity. If strong enough, they have the potential of mimicking the elliptic (and higher-order even-harmonic) flow in the di-hadron correlators: one may need to take them into account in the experimental determination of the flow observables.

Quarkonium production in high energy proton-nucleus collisions: CGC meets NRQCD

Abstract: We study the production of heavy quarkonium states in high energy proton-nucleus collisions. Following earlier work of Blaizot, Fujii, Gelis, and Venugopalan, we systematically include both small $x$ evolution and multiple scattering effects on heavy quark pair production within the Color Glass Condensate (CGC) framework. We obtain for the first time expressions in the Non-Relativistic QCD (NRQCD) factorization formalism for heavy quarkonium differential cross sections as a function of transverse momentum and rapidity. We observe that the production of color singlet heavy quark pairs is sensitive to both "quadrupole" and "dipole" Wilson line correlators, whose energy evolution is described by the Balitsky-JIMWLK equations. In contrast, the color octet channel is sensitive to dipole correlators alone. In a quasi-classical approximation, our results for the color singlet channel reduce to those of Dominguez et. al. [1]. We compare our results to those obtained combining the CGC with the color evaporation model and point to qualitative differences in the two approaches.

The initial state of heavy ion collisions

Abstract: We present a brief review of recent theoretical developments and related phenomenological approaches for understanding the initial state of heavy ion collisions, with emphasis on the Color Glass Condensate formalism.

Dynamical entropy of dense QCD states

Abstract: We discuss dense states of QCD matter formed in high-energy hadronic and heavy-ion collisions from the point of view of statistical physics of non-equilibrium processes. For this sake, we first propose a formulation of the dynamical entropy of dense QCD states in the "saturation regime" leading to a color glass condensate (CGC). The statistical physics description amounts to describe the modification of the color correlation length with energy as a compression process for which non equilibrium thermodynamic properties are applicable. We derive an expression of the dynamical entropy in terms of the rapidity evolution of the unintegrated gluon distributions in the colliding nuclei, verifying suitable positivity and irreversibility properties. We extend this approach to the initial pre-equilibrium (glasma) state of an heavy-ion collision. It allows for a definition of the initial entropy before the evolution towards the hydrodynamic regime as a function of the glasma correlation length and an overlap parameter characterizing the low-momentum spectrum of the glasma state. This initial entropy, by extension to the N=4 SYM theory, is then matched as the key input parameter to the strong coupling evaluation of thermalization towards the hydrodynamic regime based on the AdS/CFT correspondence. It thus allows to cast a bridge between the weak and strong coupling phases of an heavy-ion reaction.

The initial state of heavy-ion collisions

Abstract: We present a brief review of recent theoretical developments and related phenomenological approaches for understanding the initial state of heavy-ion collisions, with emphasis on the Color Glass Condensate formalism.

Dipole-dipole scattering in CGC/saturation approach at high energy: summing Pomeron loops

Abstract: In this paper we demonstrate that the dense system of partons (gluons) can be produced in dilute-dilute system scattering, using the example of dipole-dipole collisions. This increase in density stems from the intensive gluon cascades that can be described by the enhanced BFKL Pomeron diagrams (Pomeron loops). For the first time we found the analytical solution to the equation for diffraction production in the dipole-dense parton system scattering, using the simplified BFKL kernel. Having this solution as well as the solution to Balitsky- Kovchegov equation we developed technique that allowed us to calculate the total cross section, cross sections for single and double diffractions in the MPSI approximation. Calculating inclusive production and two gluon correlations we see that the dense and strongly correlated system of gluons can be produced at high energy in the dipole-dipole scattering.

Extra dimensions, black holes and fireballs at the LHC

Abstract: The collision of two gravitationally interacting, ultra-relativistic, extended sources is being examined. This investigation classifies the transverse distributions that are collided for fixed collision energy, according to whether one or two (a small and a large) apparent horizons may or may not be formed in a flat background in 4 dimensions. The study extends to the thermodynamical properties of the objects that are created, which exhibit a universal behavior in their entropy, and, suggests the elimination of the possibility in observing black holes (BHs) at the LHC in the absence of extra dimensions. On the other hand, including extra dimensions, and assuming that the matter is localized (dense) enough in those directions, opens new avenues in creating BHs at energies of the order of TeV. The investigation is carried further to AdS 5 backgrounds and makes connections with the implications for the quark-gluon plasma (QGP) formation in heavy ion collisions. In particular, classes of the geometries found suggest that a BH is formed if and only if the (central collision) energy is sufficiently large compared to the transverse scale of the corresponding gauge theory side stress-tensor. This implies that when the scattering in the gravity description is mapped onto a heavy ion collision problem yields a result, which is in accordance with the current intuition and data: QGP is formed only at high enough energies compared to ΛQCD, even for central processes. Incorporating weak coupling physics and in particular the Color Glass Condensate (CGC) model, a satisfactory fitting with the RHIC and the LHC data for multiplicities may be established.

From emc and cronin effects to signals of quark–gluon plasma

Abstract: The EMC and Cronin effects are explained by a unitarized evolution equation, in which the shadowing and antishadowing corrections are dynamically produced due to gluon fusions. For this sake, an alternative form of the GLR-MQ-ZRS equation is derived. The resulting gluon distributions, integrated and unintegrated, in protons and nuclei are used for analysis of the contributions of the initial part on distributions to the nuclear suppression factor in heavy-ion collisions. A simulation of the fractional energy loss is extracted from the data of RHIC and LHC, where the contributions of both nuclear shadowing and nuclear antishadowing effects are considered. We find a rapid crossover from weak energy loss to strong enegy loss with the gluon jet at a universal critical energy, E-c similar to 10GeV.

Elliptic and hexadecapole flow of charged hadrons in viscous hydrodynamics with Glauber and color glass condensate initial conditions for Pb–Pb collision at $\sqrt{s_{NN}}$ = 2.76 TeV

Abstract: The experimentally measured elliptic (v2) and hexadecapole (v4) flow of charged particles as a function of transverse momentum (pT) at midrapidity in Pb?Pb collisions at = 2.76 TeV is compared with the relativistic viscous hydrodynamic model simulations. The simulations are carried out for two different initial energy density profiles obtained from (i) the Glauber model, and (ii) the color glass condensate (CGC) model. A comparison to experimental data for 10?20% to 40?50% centrality shows that a centrality dependent shear viscosity to entropy density (?/s) ratio with values ranging between 0.0 to 0.12 is needed to explain the v2 data for simulations with the Glauber based initial condition, whereas for the CGC based initial conditions a slightly higher value of ?/s is preferred, around 0.08 to 0.16. From the comparison of the v4 simulated results to the corresponding experimental measurements we observe that for the centralities 20?30% to 40?50% the ?/s values lie between 0.0 to 0.12 for both the initial conditions studied. The ?/s values obtained from our studies for Pb?Pb collisions at = 2.76 TeV are compared to other studies which use both transport and hydrodynamic approaches.

Next-to-leading order correction to inclusive particle spectra in the color glass condensate framework

Abstract: In [arXiv:0804.2630], we have analyzed the leading logarithms of energy that appear in the inclusive spectrum of gluons produced in heavy ion collisions, calculated in the Color Glass Condensate framework. The main result of this paper was that these logarithms are intrinsic properties of the colliding projectiles, and that they can be resummed by letting the distributions of color sources in the nuclei evolve according to the JIMWLK equation. An essential step in the proof of this factorization result is the calculation of the gluon spectrum at Next-to-Leading order, and in particular a functional relationship that expresses the NLO correction as the action of a certain operator on the LO spectrum. In this paper, we show that this type of relation between spectra at LO and NLO is not specific to the production of gluons, but that it is in fact generic for inclusive spectra in heavy ion collisions. To illustrate this, we compute up to NLO the inclusive spectrum of some hypothetical scalar fields, either color neutral or colored, that couple to gluons.

High density effects in ultrahigh neutrino interactions

Abstract: The high parton density present at high energies and large nuclei is expected to modify the lepton-hadron cross section and the associated observables. In this paper we analyze the impact of the high density effects in the average inelasticity and the neutrino-nucleus cross section at ultrahigh energies. We compare the predictions associated to the linear Dokshitzer-Gribov-Lipatov-Altarelli-Parisi dynamics with those from the color glass condensate formalism, which includes nonlinear effects. Our results demonstrated that the nonlinear effects reduce the average inelasticity and that the predictions of the distinct approaches for the neutrino-nucleus cross section at ultrahigh energies are similar.

High density effects in ultrahigh neutrino interactions

Abstract: The high parton density present at high energies and large nuclei is expected to modify the lepton - hadron cross section and the associated observables. In this paper we analyse the impact of the high density effects in the average inelasticity and the neutrino - nucleus cross section at ultra high energies. We compare the predictions associated to the linear DGLAP dynamics with those from the Color Glass Condensate formalism, which includes non-linear effects. Our results demonstrated that the non-linear effects reduce the average inelasticity and that the predictions of the distinct approaches for the neutrino - nucleus cross section at ultra-high energies are similar.

Comparing Two Different Initial Conditions AAMQS and Quartic Action in Illustrating the Effect of Valence Color Charges in High-Energy Collisions at Forward Rapidity

Abstract: The inclusive particle productions in proton-proton ( ) and deuton-gold ( +Au) collisions at forward rapidity at the Relativistic Heavy Ion Collider (RHIC) energy are studied in the framework of the color glass condensate (CGC) theory by using two different initial conditions: AAMQS (Albacete-Armesto-Milhano-Quiroga-Salgado) and quartic action. Then, the results obtained by the two different initial conditions in illustrating the effect of valence color charges in high-energy proton-nucleus ( ) collisions at forward energy are compared. Meanwhile, the inclusive particle productions in collisions at forward rapidity at the Large Hadron Collider (LHC) energies are predicted. The main dynamical input in our calculations is the use of solutions of the running coupling Balitsky-Kovchegov equation tested in electron-proton ( ) collision data. Particle production is computed via the hybrid formalisms to obtain spectra and yields. These baseline predictions are useful for testing the current understanding of the dynamics of very strong color fields against the upcoming LHC data.

Determination of the Parameters of a Color Neutral 3D Color Glass Condensate Model

Abstract: We consider a version of the McLerran-Venugopalan model by Lam and Mahlon where confinement is implemented via colored noise in the infrared. This model does not assume an infinite momentum frame, hence the boosted nuclei are not infinitely thin. Instead, the nuclei have a finite extension in the longitudinal direction and therefore depend on the longitudinal coordinate. In this fully three-dimensional framework an x dependence of the gluon distribution function emerges naturally. In order to fix the parameters of the model, we calculate the gluon distribution function and compare it with the JR09 parametrization of the data. We explore the parameter space of the model to attain a working framework that can be used to calculate the initial conditions in heavy ion collisions.