arXiv subjects

M. V. T. Machado

Publications and source records attributed to M. V. T. Machado.

At least 19 recordsLinked to original sources

arXiv2025

Universality of scaling entropy in charged hadron multiplicity distributions at the LHC

In this work, we investigate the scaling behavior of the entropy associated with the charged hadron multiplicity distribution P(N) in proton-proton collisions at the LHC. We show that the growth of this entropic indicator as a function of the Bjorken x variable exhibits a universal behavior, consistent with observations from deep inelastic scattering (DIS). This universality suggests that the entropy scaling is a property of the initial state and reflects the diffusive nature of gluon dynamics at small x. Furthermore, we demonstrate that high-multiplicity events are not accurately described by traditional KNO scaling and require a more precise description based on a diffusion scaling framework. This new scaling emerges naturally from the universal growth of partonic entropy and offers a deeper insight into the dynamics of particle production in high-energy hadronic collisions.

hep-ph↗

arXiv2025

Investigating QCD Dynamical Entropy in high-energy nuclear collisions

In this work, the concept of QCD dynamical entropy is extended to heavy ion systems. This notion of entropy can be understood as a relative entropy and can also be used to estimate the initial entropy density in ultra-relativistic heavy ion collisions. The key quantity used to calculate this entropy is the nuclear unintegrated gluon distribution (nUGD), which provides a transverse momentum probability density. In the numerical analysis, both the geometric scaling phenomenon and the Glauber-Gribov approach have been used to evaluate realistic models for the nUGD. It is shown that the normalization procedure and the geometric scaling property make the dynamical entropy almost independent of the nucleus mass number $A$. Results are presented for the dynamical entropy density, $dS_D/dy$, in terms of the rapidity.

hep-ph↗

arXiv2025

Testing the double-logarithm asymptotic gluon density in ultraperipheral heavy ion collisions at the Large Hadron Collider

In this paper, we analyze the application of an analytical gluon distribution based on double-asymptotic scaling to the photoproduction of vector mesons in coherent $pp$, $pA$, and $AA$ collisions at LHC energies, using the color dipole formalism. Predictions for the rapidity distribution are presented for $ρ^0$, $J/ ψ$, $ψ(2S)$, and $Υ(1S)$ mesons photoproduction. An analysis of the uncertainties associated with different implementations of the dipole--proton amplitude is performed. The vector meson photoproduction accompanied by electromagnetic dissociation is also analyzed.

hep-ph↗

arXiv2025

The glue that binds us all -- Latin America and the Electron-Ion Collider

The Electron-Ion Collider, a next generation electron-hadron and electron-nuclei scattering facility, will be built at Brookhaven National Laboratory. The wealth of new data will shape research in hadron physics, from nonperturbative QCD techniques to perturbative QCD improvements and global QCD analyses, for the decades to come. With the present proposal, Latin America based physicists, whose expertise lies on the theory and phenomenology side, make the case for the past and future efforts of a growing community, working hand-in-hand towards developing theoretical tools and predictions to analyze, interpret and optimize the results that will be obtained at the EIC, unveiling the role of the glue that binds us all. This effort is along the lines of various initiatives taken in the U.S., and supported by colleagues worldwide, such as the ones by the EIC User Group which were highlighted during the Snowmass Process and the Particle Physics Project Prioritization Panel (P5).

nucl-ex↗

arXiv2024

Multiplicity dependence of the $p_T$-spectra for charged particles and its relationship with partonic entropy

We investigate the multiplicity dependence of the transverse momentum $p_T$ spectra of hadrons produced in high-energy collisions. We propose that the partonic distribution be parameterized by its non-extensive entropy and the parton saturation scale $Q_s(x)$. These two variables can be identified from the produced charged hadron distributions and provide important information on the gluon dynamics at the moment of interaction. From this perspective we interpret data from different ALICE multiplicity classes at $\sqrt{s}= 13$ TeV and $\sqrt{s}= 5.02$ TeV. A multiplicity dependent scaling function is presented and the dependence of the interaction area on multiplicity is also investigated.

hep-ph↗

arXiv2023

Double charmed meson production in $pp$ and $pA$ collisions at the LHC within the dipole approach in momentum representation

A study of double charmed meson production in proton-proton and proton-nucleus collisions at the LHC energies is performed. Based on the color dipole formalism developed in the transverse momentum representation and the double parton scattering mechanism, predictions are made for the transverse momentum differential cross section for different pairs of $D$-mesons. The theoretical results consider the center-of-mass energy and forward rapidities associated to the measurements by the LHCb Collaboration. The results considering different unintegrated gluon distributions are presented and compared to data and predictions for proton-nucleus collisions are provided.

hep-ph↗

arXiv2023

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

We present an analysis of the most precise set of HERA data within the color dipole formalism, by using an analytical gluon density, based on the double-logarithm approximation of the DGLAP equations in the asymptotic limit of the scaling variable, $σ=\log{(1/x)}\log{(\log{(Q^2/Q_ 0^2)})}\rightarrow \infty$. Fits to data, including charm and bottom quarks are performed and demonstrate the efficiency of the model in describing the reduced cross section, $σ_{r}$, in the wide range $Q^2:(1.5,500)$ GeV$^2$ for two dipole models including parton saturation effects. We also give predictions to $F_{2}^{c\bar{c}}$ , $F_{2}^{b\bar{b}}$ and $F_{L}$, all describing the data reasonably well in the range $Q^2:(2.5,120)$ GeV$^2$. 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.

hep-ph↗

arXiv2022

$D$-meson production in high energy $pA$ collisions within the QCD color dipole transverse momentum representation

The $D$-meson production is investigated by considering the unintegrated gluon distribution within the dipole approach in the momentum representation. We analyze the $D$-meson spectrum accounting for the effects of nonlinear behavior of the QCD dynamics which can be accordingly addressed in the dipole framework. The unintegrated gluon distribution is obtained by using geometric scaling property and the results are compared to the Glauber-Gribov framework. The absolute transverse momentum spectra and the nuclear modification ratios are investigated. Predictions are compared with the experimental measurements by the ALICE and LHCb Collaborations in $pA$ collisions for different rapidity bins.

hep-ph↗

arXiv2022

Nuclear Modification Factor in Small System Collisions within Perturbative QCD Including Thermal Effects

In this paper, dedicated to the memory of the late Prof. Jean Cleymans, the nuclear modification factors, $R_{xA}$, are investigated for pion production in small system collisions, measured by PHENIX experiment at RHIC (Relativistic Heavy Ion Collider). The theoretical framework is the transverse momentum $k_T$-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 $R_{xA}$ at large transverse momentum, $p_T$. The multiplicity of produced particles, which is sensitive to the soft sector of the spectra, is also included in the present analysis.

hep-ph↗

arXiv2022

Exclusive $Z^0$ production in $ep$ and $eA$ collisions at high energies

In this work the $k_{\perp}$-factorization formalism is applied to compute the exclusive $Z^0$ boson photoproduction in $ep$ and $eA$ collisions. The study is also extended to $pp$ and $AA$ processes. The nuclear effects are investigated considering heavy and light ions. Analytical models for the unintegrated gluon distribution are taken into account and the corresponding theoretical uncertainty is quantified. The analysis is done for electron-ion collisions at the Large Hadron-Electron Collider (LHeC), its high-energy upgrade (HE-LHeC) and at the Future Circular Collider (FCC) in lepton-hadron mode. Additionally, ultra-peripheral heavy ion collisions at future runs of the Large Hadron Collider (LHC) and at the FCC (hadron-hadron mode) are also considered.

hep-ph↗

arXiv2022

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 $ΔY = Y-Y_0$ given an initial rapidity $Y_0$. The theoretical uncertainties are investigated and comparison with related approaches in literature is done.

hep-ph↗

arXiv2022

Nuclear transverse momentum imbalance in the color dipole approach at the LHC regime

Transverse momentum broadening of a parton propagating through a large nucleus is evaluated in the color dipole approach using different models for the dipole cross section or unintegrated gluon distribution, which lead to different values of the coefficient $C_{\mathcal{F}}(0,s)$. Numerical calculations are compared to data extracted from LHCb and ALICE experiments for nuclear broadening of $J/ψ$. We find that different models which describe the small-$x$ data predict values of $Δp_T^2$ that agree reasonably well with experiment, specially for forward rapidity. The centrality dependence was also analysed and the models are consistent with the ALICE measurements.

hep-ph↗

arXiv2022

Hard gluon evolution in the last stage of the bottom-up thermalization

The study of how fast thermalization in heavy ion collisions occurs has been one of the central topics in the heavy ion community. In the weak coupling picture this thermalization occurs from "the bottom 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. In this scheme we apply a model on parton energy loss to discuss the effects of medium expansion on the thermalization problem and estimate the average transverse momentum diffusivity for thermalization in a Bjorken expanding medium.

hep-ph↗

arXiv2022

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 probabilistic perturbative approach. The results were applied to the thermalization problem in heavy ion collisions, in the third stage of the bottom-up picture, to estimate the initial time for the third stage of the bottom-up scenario. We then look at the entropy density and average temperature of the soft thermal bath, as the system approaches (local) thermal equilibrium.

hep-ph↗

arXiv2021

Charmed meson production based on dipole transverse momentum representation in high energy hadron-hadron collisions available at the LHC

The production of $D$-mesons in high-energy $pp$ collisions at the LHC kinematic regime is analyzed with the dipole approach in the momentum representation. We present predictions for the $D$-meson differential cross section in terms of the transverse momentum and rapidity distributions taking into account the nonlinear behavior of the QCD dynamics. Comparison between our results and the corresponding experimental measurements reported by the ALICE and LHCb Collaborations in different rapidity bins is performed. We show that the $D$-meson production in the high energy limit can be properly addressed by using the QCD dipole transverse momentum distributions.

hep-ph↗

arXiv2021

QCD traveling waves phenomenology revisited

In this paper we review and update the Amaral-Gay Ducati-Betemps-Soyez saturation model, by testing it against the recent H1-ZEUS combined data on deep inelastic scattering, including heavy quarks in the dipole amplitude. We obtain that this model, which is based on traveling wave solutions of the Balitsky-Kovchegov equation and built in the momentum space framework, yields very accurate descriptions of the reduced cross section, $σ_{r}(x,y,Q^{2})$, as well as DIS structure functions such as $F_{2}(x,Q^{2})$ and $F_{L}(x,Q^{2})$, all measured at HERA. Additionally, it provides good descriptions of heavy quark structure functions, $F_{2}^{cc}$ and $F_{2}^{bb}$ at small-$x$ and $Q^{2}\lesssim 60$ GeV$^{2}$. We also use the improved model to make predictions for structure functions to be measured in the near future at LHeC.

hep-ph↗

arXiv2021

Role of nuclear gluon distribution on particle production in heavy ion collisions

The transverse momentum spectra of hadrons is calculated from the unintegrated gluon distribution (UGD) within the $k_T$-factorization framework at small $x$. Starting from $pp$ collisions, the modification caused by the nuclear medium is incorporated in the UGD at high energies, which is related to the nuclear shadowing phenomenon. Moreover, we consider that particle production from minijet decaying is not enough to explain the $p_T$ spectra in $AA$ collisions due to collective phenomena that take place after the hard collision. The Boltzmann-Gibbs Blast Wave (BGBW) distribution is utilized in order to evaluate the distribution of particle production in equilibrium. Data from ALICE collaboration for $PbPb$ collisions at $\sqrt{s}=2.76$ TeV are analyzed and the nuclear modification factor for pion production is computed.

hep-ph↗

arXiv2021

Exclusive dilepton production via timelike Compton scattering in heavy ion collisions

In the present work, $k_T$-factorization formalism is applied to compute the exclusive dilepton production by timelike Compton scattering (TCS) in $eA$, $pA$ and $AA$ collisions. The nuclear effects are investigated considering heavy and light ions. The production cross section in terms of invariant mass and rapidity distribution of the lepton pair is shown. The analysis is done for electron-ion collisions at the Large Hadron-Electron Collider (LHeC), its high-energy upgrade (HE-LHeC) and at the Future Circular Collider (FCC) in lepton-hadron mode. Additionally, ultraperipheral heavy ion collisions at future runs of the Large Hadron Collider (LHC) and at the FCC (hadron-hadron mode) are also considered.

hep-ph↗