Investigating Fl (x, Q2) at fixed energy in the color dipole formalism

At small x, the structure function FL(x,Q2) is driven by the gluon content of the nucleon target and consequently it can unravel the underlying QCD dynamics in that region. In this work, one studies its behavior on the photon virtuality Q2 at fixed energy within the color dipole formalism for models considering parton saturation effects. The reason is that they resum a wide class of higher-twist contributions, which have an important influence on the FL description towards low Q2. It is shown that the geometric scaling property holds for the longitudinal cross section. Moreover, the effective anomalous dimension in the scaling dipole cross sections can be investigated by studing both the turn-over and the large Q2 regions of the recent experimental measurements

Nuclear modification factor in small system collisions within perturbative QCD including thermal effects

In this paper, the nuclear modification factors, RxA, are investigated for pion production in small system collisions, measured by PHENIX experiment at RHIC (Relativistic Heavy Ion Collider). The theoretical framework is the parton transverse momentum kT-factorization formalism for hard processes at small momentum fraction, x. Evidence for collective expansion and thermal effects for pions, produced at equilibrium, is studied based on phenomenological parametrization of blast-wave type in the relaxation time approximation. The dependencies on the centrality and on the projectile species are discussed in terms of the behavior of Cronin peak and the suppression of RxA at large transverse momentum, pT. The multiplicity of produced particles, which is sensitive to the soft sector of the spectra, is also included in the present analysis

Investigating the QCD dynamical entropy in high-energy hadronic collisions

The dynamical entropy of dense gluonic states in proton-proton collisions at high energies is studied by using phenomenological models for the unintegrated gluon distribution. The corresponding transverse momentum probability distributions are evaluated in terms of rapidity. The dynamical entropy density is obtained in the rapidity range relevant for the collisions at the Large Hadron Collider. The total entropy density for the dense system is computed as a function of the rapidity evolution ΔY ¼ Y − Y0 given an initial rapidity Y0. The theoretical uncertainties are investigated, and a comparison with related approaches in literature is done

Hard gluon evolution in warming medium

We describe the energy distribution of hard gluons travelling through a dense quark–gluon plasma whose temperature increases linearly with time, within a probabilis tic perturbative approach. The results were applied to the thermalization problem in heavy ion collisions. In the weak coupling picture this thermalization occurs from “the bot tom up”: high energy partons, formed early in the collision, radiate low energy gluons which then proceed to equilibrate among themselves, forming a thermal bath that brings the high energy sector to equilibrium. We see that, in this sce nario, the dynamic we describe must set in around t ∼ 0.5 fm/c after the collision in order to reach a fully thermalized state at t ∼ 1 fm/c. We then look at the entropy density and average temperature of the soft thermal bath, as the system approaches (local) thermal equilibrium

Investigating entanglement entropy at small x in DIS off protons and nuclei

In this work we analyze the entanglement entropy in deep inelastic scattering off protons and nuclei. It is computed based on the formalism where the partonic state at small-x is maximally entangled with proton being constituted by large number of microstates occurring with equal probabilities. We consider analytical expressions for the number of gluons, Ngluon, obtained from gluon saturation models for the dipole-target amplitudes within the QCD color dipole picture. In particular, the nuclear entanglement entropy per nucleon is studied. We also study the underlying uncertainties on these calculations and compare the results to similar investigations in literature

Asymptotic gluon density within the color dipole picture in light of HERA high-precision data

We present an analysis of the most precise set of Hadron-Electron Ring Accelerator (HERA) data within the color dipole formalism, by using an analytical gluon density, based on the double-logarithm approximation of the Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) equations in the asymptotic limit of the scaling variable, σ ¼ log ð1=xÞlog ðlog ðQ2=Q2 0ÞÞ → ∞. Fits to the data, including charm and bottom quarks, are performed and demonstrate the efficiency of the model in describing the reduced cross section, σr, in the wide range Q2∶ ð1.5; 500Þ GeV2 for two dipole models including parton saturation effects. We also give predictions to Fcc¯ 2 , Fbb¯ 2 and FL, all describing the data reasonably well in the range Q2∶ ð2.5; 120Þ GeV2. Total cross sections of exclusive photoproduction of J=ψ and ρ are also calculated and successfully compared to HERA data and recent measurements at LHCb

Double meson production in ultraperipherical heavy-ion collisions

The double-meson production in ultraperipheral heavy-ions collisions is addressed, focusing on the particular case of ρJ/Ψ from two-photon reactions. The cross section at photon level is obtained using distinct parameterizations for the gluon distribution on the light meson. The resulting estimates for the nuclear case are presented and discussed. As a by-product, we estimate the double ρ production cross section using the pomeron-exchange factorization relations

The QCD pomeron in ultraperipheral heavy ion collisions : I. The double J/Ψ production

The contribution of the QCD pomeron to the process AA → AAJ/Ψ J/Ψ is discussed. We focus on the photon–photon collision, with the quasi-real photon coming from theWeizs¨acker–Williams spectrum of the nuclei. We calculate the cross section for this process considering the solution of the LLA BFKL equation at zero momentum transfer using a small t approximation for the differential cross section of the subprocess. Furthermore, the impact of non-leading corrections to the BFKL equation is also analyzed. In both cases the cross section is found to increase with the energy, predicting considerable values for the LHC energies. Moreover, we compare our results with the Born two-gluon approximation, which is energy independent at the photon level. Our results indicate that the experimental analyses of this process can be useful to discriminate the QCD dynamics at high energies

Nuclear exclusive vector meson photoproduction

We calculate the nuclear cross section for vector meson exclusive photoproduction within the QCD color dipole picture and in the Regge approach. For the former approach, we have considered the phenomenological saturation model, whereas for the latter we use a model based on the dipole pomeron framework. Theoretical estimates for scattering on both light and heavy nuclei are given over a large range of energy

Dilepton production through timelike compton scattering within the kT-factorization approach

In this work we consider the dilepton production via timelike Compton scattering (TCS) in electronproton and proton-proton collisions. In particular, the differential cross section in terms of the dilepton invariant mass and rapidity is computed within the kT-factorization approach. Besides, we utilize distinct unintegrated gluon distributions (UGD) in order to compare their impact on the differential cross section of TCS in pp (ep) collisions evaluated at the LHC (LHeC), HL-LHC (LHeC), HE-LHC (LHeC), and FCC-hh (eh) center-of-mass energie