Fabio Dominguez

Universality of Unintegrated Gluon Distributions at small x

We systematically study dijet production in various processes in the small-x limit and establish an effective kt-factorization for hard processes in a system with dilute probes scattering on a dense target. In the large-Nc limit, the unintegrated gluon distributions involved in different processes are shown to be related to two widely proposed ones: the Weizsacker-Williams gluon distribution and the dipole gluon distribution.

Comparing energy loss and p⊥-broadening in perturbative QCD with strong coupling N=4 SYM theory☆

Abstract We compare medium induced energy loss and p ⊥ -broadening in perturbative QCD with that of the trailing string picture of SYM theory. We consider finite and infinite extent matter as well as relativistic heavy quarks which correspond to those being produced in the medium or external to it. When expressed in terms of the appropriate saturation momentum, we find identical parametric forms for energy loss in perturbative QCD and SYM theory. We find simple correspondences between p ⊥ -broadening in QCD and in SYM theory although p ⊥ -broadening is radiation dominated in SYM theory and multiple scattering dominated in perturbative QCD.

kt-factorization for Hard Processes in Nuclei

Two widely proposed k(t)-dependent gluon distributions in the small-x saturation regime are investigated using two-particle back-to-back correlations in high energy scattering processes. The Weizsäcker-Williams gluon distribution, interpreted as the number density of gluon inside 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.

Medium-induced gluon branching

A bstractWe study the evolution of an energetic jet which radiates gluons while propagating through a dense QCD medium modeled as a random distribution of color sources. Motivated by the heavy ion experimental program at the LHC, we focus on the medium induced radiation of (relatively) soft gluons, which are abundantly emitted at large angles and thus can transport a small fraction of the jet energy far away from the jet axis. We perform a complete calculation of the medium-induced gluon branching in the regime where the gluons that take part in the branching undergo multiple soft scattering with the medium. We extend the BDMPSZ theory of radiative energy loss by including the transverse momentum dependence in the kernel that describes the branching and by analyzing the correlations between the two offspring gluons. We demonstrate that these gluons lose color coherence with respect to each other over a time scale that is comparable to the duration of the branching. It follows that interference effects between successive emissions are suppressed, a necessary ingredient for a description of multiple emission of soft gluons by a probabilistic, branching process.

Probabilistic picture for medium-induced jet evolution

A bstractA high energy jet that propagates in a dense medium generates a cascade of partons that can be described as a classical branching process. A simple generating functional for the probabilities to observe a given number of gluons at a given time is derived. This is used to obtain an evolution equation for the inclusive one-gluon distribution, that takes into account the dependence upon the energy and the transverse momentum of the observed gluon. A study of the explicit transverse momentum dependence of the splitting kernel leads us to identify large corrections to the jet quenching parameter

On the small-x evolution of the color quadrupole and the Weizsäcker–Williams gluon distribution

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Universality of multiparticle production in QCD at high energies

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On dissociation of heavy mesons in a hot quark–gluon plasma

Abstract Color quadrupoles have been found to be important in the proper description of observables sensitive to the small- x regime in nuclei as well as in the operator definition of the Weizsacker–Williams gluon distribution. In this Letter, we derive the small- x evolution equation of the quadrupole and the Weizsacker–Williams gluon distribution without taking the large N c limit and study the properties of the equation in both dilute and saturation regime. We find that the quadrupole evolution follows the BFKL evolution in the dilute regime and then saturates in the dense region due to nonlinear terms. This leads us to conclude that the Weizsacker–Williams gluon distribution should obey the same geometrical behavior as the dipole gluon distribution as found in the inclusive DIS measurement.

Gluon Saturation effects on the color singlet J/ψ production in high energy dA and AA collisions

By studying the color structure of multiparticle production processes in p+A-type (dilute-dense) collisions, we find that higher-point functions beyond typical dipoles and quadrupoles, e.g., sextupoles, octupoles, etc., naturally appear in the cross sections, but are explicitly suppressed in the large-Nc limit. We evaluate the sextupole in the McLerran-Venugopalan model and find that, in general, its analytical form cannot be written as combination of dipoles and quadrupoles. Within the color glass condensate framework, we present a proof that in the large-Nc limit, all multiparticle production processes in the collision of a dilute system off a dense system can, up to all orders in αs, be described in terms of only dipoles and quadrupoles.

On multiple scatterings of mesons in hot and cold QCD matter

Abstract We compare two mechanisms for the dissociation of heavy mesons in an infinite quark–gluon plasma: dynamic Debye screening and multiple scattering. Using the uncertainty principle inspired by a Schrodinger-like equation, we find that the criterion a B ≃ 1 / μ ≃ 1 α eff 1 / 2 T with α eff ≡ α ( N c + N f 2 ) is parametrically true both for the dissociation of fast moving heavy mesons with a size a B due to dynamic Debye screening as well as for mesons at rest in the medium. In contrast, we find that the criterion for the dissociation of heavy mesons due to uncorrelated multiple scattering is parametrically a B ≃ 1 [ γ α eff ln 1 α eff ] 1 / 3 T . Therefore, multiple scattering is a more efficient mechanism for the dissociation of heavy mesons in an infinite hot plasma.