arXiv subjects

Fabio Dominguez

Publications and source records attributed to Fabio Dominguez.

36 records · Page 2Linked to original sources

arXiv2020

Simple implementation of color coherence for the resumation of soft BDMPS-Z gluons

The evolution of QCD jets under the influence of a dense colored medium leads to the non trivial modification of the gluon emission spectrum. In the multiple soft scattering regime, for sufficiently large media, soft and wide angle emissions can be resummed (in the planar limit of QCD) due to the small formation time of each gluon emission. Similarly to DGLAP evolution, such cascades correspond to pure Markovian processes and interferences between partons are neglected. In this strict limit, color coherence effects are absent. In the vacuum this coherence effect is critical to guarantee that the shower is angular ordered. In the medium, it is known that such color coherence effects might play a role in suppressing radiation at intermediate emission angles. We present a simple procedure to implement color (de)coherence effects into the in-medium evolution equations obtained in the pure Markovian approximation. We verify that the result obtained is in accordance with previous studies regarding the role of in-medium color coherence in the evolution of the QCD antenna. The new evolution equation incorporates a novel emission kernel which enforces color coherence between emitters.

hep-ph↗

arXiv2020

Medium-induced gluon radiation with full resummation of multiple scatterings for realistic parton-medium interactions

The new precision era of jet quenching observables at both RHIC and the LHC calls for an improved and more precise description of in-medium gluon emissions. The development of new theoretical tools and analytical calculations to tackle this challenge has been hampered by the inability to include the effects of multiple scatterings with the medium using a realistic model for the parton-medium interactions. In this paper, we show how the analytical expressions for the full in-medium spectrum, including the resummation of all multiple scatterings, can be written in a form where the numerical evaluation can be easily performed without the need of the usually employed harmonic or single hard approximations. We present the transverse momentum and energy-dependent medium-induced gluon emission distributions for known realistic interaction models to illustrate how our framework can be applied beyond the limited kinematic regions of previous calculations.

hep-ph↗

arXiv2020

Novel tools and observables for jet physics in heavy-ion collisions

Studies of fully-reconstructed jets in heavy-ion collisions aim at extracting thermodynamical and transport properties of hot and dense QCD matter. Recently, a plethora of new jet substructure observables have been theoretically and experimentally developed that provide novel precise insights on the modifications of the parton radiation pattern induced by a QCD medium. This report, summarizing the main lines of discussion at the 5th Heavy Ion Jet Workshop and CERN TH institute "Novel tools and observables for jet physics in heavy-ion collisions" in 2017, presents a first attempt at outlining a strategy for isolating and identifying the relevant physical processes that are responsible for the observed medium-induced jet modifications. These studies combine theory insights, based on the Lund parton splitting map, with sophisticated jet reconstruction techniques, including grooming and background subtraction algorithms.

hep-ph↗

arXiv2019

Mapping collinear in-medium parton splittings

We map the spectrum of $1\to 2$ parton splittings inside a medium characterized by a transport coefficient $\hat q$ onto the kinematical Lund plane, taking into account the finite formation time of the process. We discuss the distinct regimes arising in this map for in-medium splittings, pointing out the close correspondence to a semi-classical description in the limit of hard, collinear radiation with short formation times. Although we disregard any modifications of the original parton kinematics in course of the propagation through the medium, subtle modifications to the radiation pattern compared to the vacuum baseline can be traced back to the physics of color decoherence and accumulated interactions in the medium. We provide theoretical support to vacuum-like emissions inside the medium by delimiting the regions of phase space where it is dominant, identifying also the relevant time-scales involved. The observed modifications are shown to be quite general for any dipole created in the medium.

hep-ph↗

arXiv2019

The Color Glass Condensate density matrix: Lindblad evolution, entanglement entropy and Wigner functional

We introduce the notion of the Color Glass Condensate (CGC) density matrix $\hatρ$. This generalizes the concept of probability density for the distribution of the color charges in the hadronic wave function and is consistent with understanding the CGC as an effective theory after integration of part of the hadronic degrees of freedom. We derive the evolution equations for the density matrix and show that the JIMWLK evolution equation arises here as the evolution of diagonal matrix elements of $\hatρ$ in the color charge density basis. We analyze the behavior of this density matrix under high energy evolution and show that its purity decreases with energy. We show that the evolution equation for the density matrix has the celebrated Kossakowsky-Lindblad form describing the non-unitary evolution of the density matrix of an open system. Additionally, we consider the dilute limit and demonstrate that, at large rapidity, the entanglement entropy of the density matrix grows linearly with rapidity according to $d S_e / d y = γ$, where $γ$ is the leading BFKL eigenvalue. We also discuss the evolution of $\hatρ$ in the saturated regime and relate it to the Levin-Tuchin law and find that the entropy again grows linearly with rapidity, but at a slower rate. By analyzing the dense and dilute regimes of the full density matrix we are able to establish a duality between the regimes. Finally we introduce the Wigner functional derived from this density matrix and discuss how it can be used to determine the distribution of color currents, which may be instrumental in understanding dynamical features of QCD at high energy.

hep-ph↗

arXiv2019

Radiative corrections to the jet quenching parameter in dilute and dense media

We extend the calculation of radiative corrections to momentum broadening in a QCD medium to include processes where single scattering dominates over multiple soft scatterings. Our analysis focusses on processes that are enhanced by a potentially large double logarithmic contribution. We demonstrate that such double logarithmic contributions emerge in calculations of momentum broadening in dilute systems where only single scattering occurs. We show how the different regimes, multiple versus single scattering, constrain different parts of the phase space.

hep-ph↗

arXiv2017

Quark-antiquark antenna splitting in a medium

We study a system in which a quark-antiquark antenna emits a hard gluon in a medium, and an extra very soft emission afterwards. Considering the coherence effects in terms of the survival probability, we can describe the interaction of the $q\bar{q}g$ configuration with the medium. We extrapolate previous analyzes of the antenna radiation to the case of two hard splittings inside the medium, and prove that this generalization keeps back the picture of jet quenching with effective emitters in the parton QCD cascade.

hep-ph↗

arXiv2013

Probabilistic picture for medium-induced jet evolution

A 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.

hep-ph↗

arXiv2013

Universality of multi-particle production in QCD at high energies

By studying the color structure of multi-particle 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-N_c 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-N_c limit, all multi-particle production processes in the collision of a dilute system off a dense can, up to all orders in α_s, be described in terms of only dipoles and quadrupoles.

hep-ph↗

arXiv2012

Medium-induced gluon branching

We 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.

hep-ph↗

arXiv2012

On the linearly polarized gluon distributions in the color dipole model

We show that the linearly polarized gluon distributions appear in the color dipole model as we derive the full cross sections of the DIS dijet production and the Drell-Yan dijet ($γ^*$ jet correlation) process. Together with the normal Weizsäcker-Williams gluon distribution, the linearly polarized one will contribute to the DIS dijet production cross section as the coefficient of the $\cos(2 Δϕ) $ term in the correlation limit. We also derive the exact results for the cross section of the Drell-Yan dijet process, and find that the linearly polarized dipole gluon distribution which is identical to the normal dipole gluon distribution involves in the cross section. The results obtained in this paper agree with the previous transverse momentum dependent factorization study. We further derive the small-$x$ evolution of these linearly polarized gluon distributions and find that they rise as $x$ gets small at high energy.

hep-ph↗

arXiv2011

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

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 Weizsäcker-Williams gluon distribution. In this paper, we derive the small-x evolution equation of the quadrupole and the Weizsäcker-Williams gluon distribution without taking 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 Weizsäcker-Williams gluon distribution should obey the same geometrical behavior as the dipole gluon distribution as found in the inclusive DIS measurement.

hep-ph↗

arXiv2011

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 $k_t$-factorization for hard processes in a system with dilute probes scattering on a dense target. We find that the well-known Weizsäcker-Williams gluon distribution can be directly probed in the quark-antiquark jet correlation in deep inelastic scattering and the dipole gluon distribution can be directly measured in the direct photon-jet correlation in $pA$ collisions. In the large-$N_c$ limit, the unintegrated gluon distributions involved in other different dijet channels in pA collisions are shown to be related to two widely proposed ones: the Weizsäcker-Williams gluon distribution and the dipole gluon distribution.

hep-ph↗

arXiv2011

kt-factorization for Hard Processes in Nuclei

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.

hep-ph↗

arXiv2010

Particle production in DIS off a shockwave in AdS

Within the AdS/CFT correspondence, the shockwave metric has been widely used as a gravity dual for a fast moving nucleus. Here we propose a picture for particle production in deep inelastic scattering off a shockwave with the projectile represented by the $\mathcal{R}$-current. By using the method developed in \cite{Avsar:2009xf} to find an explicit expression for the scattered field, we are able to show that the scattered field can be written in terms of time-like and space-like vacuum states where the time-like states are identified with the outgoing particles. To support this picture, we calculate the contribution of the time-like modes to the energy-momentum tensor of the scattered field and show that the energy flow in the fifth dimension is directly related to the imaginary part of the action. The energy flow in the fifth dimension is also compared to the incoming energy flow to determine which fraction of the initial energy goes to the produced particles. The last two sections are devoted to localize the energy flow in momentum and coordinate space, first by finding the virtualities that contribute the most to the total flow, and second by finding an approximate trajectory in coordinate space.

hep-th↗

arXiv2009

On multiple scatterings of mesons in hot and cold QCD matter

We study the propagation of a color singlet q\bar{q} pair undergoing multiple scatterings in hot and cold QCD matter. The interaction of the dipole with the nucleus or plasma is described with the McLerran-Venugopalan and Gyulassy-Wang models respectively. We find identical results when expressed in terms of the saturation momentum of either the nucleus or the plasma. We compare two kinds of multiple scatterings, elastic and inelastic with respect to the target. When allowing the target to scatter inelastically, the difference with the elastic case is suppressed by a 1/N^2_c factor. We also discuss some implications of our results in the following situations: the survival probability of quarkonia in a hot medium, the production of high-p_T heavy mesons in nucleus-nucleus collisions, and the production of vector mesons in deep inelastic scattering off nuclei.

nucl-th↗

arXiv2008

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

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\simeq1/μ\simeq 1/(α_{eff}^{1/2}T) with α_{eff}\equivα(N_c+{N_f\over2}) 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 1/a_B \simeq [γα_{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.

hep-ph↗

arXiv2008

Comparing energy loss and $p_{\perp}$-broadening in perturbative QCD with strong coupling $\mathcal{N}=4$ SYM theory

We compare medium induced energy loss and $p_{\perp}$-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 $p_{\perp}$-broadening in QCD and in SYM theory although $p_{\perp}$-broadening is radiation dominated in SYM theory and multiple scattering dominated in perturbative QCD.

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