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M. V. T. Machado

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

At least 127 records · Page 7Linked to original sources
arXiv2003

Phenomenology on the QCD dipole picture revisited

We perform an adjust to the most recent structure function data, considering the QCD dipole picture applied to ep scattering. The structure function F2 at small x and intermediate Q2 can be described by the model containing an economical number of free-parameters, which encodes the hard Pomeron physics. The longitudinal structure function and the gluon distribution are predicted without further adjustments. The data description is effective, whereas a resummed next-to-leading level analysis is deserved.

hep-ph↗
arXiv2003

Nuclear charm and bottom production: a comparison among high energy approaches

We calculate the nucleon and nuclear photoproduction cross sections for heavy quarks within the $k_{\perp}$-factorization formalism, considering the current high energy approaches which include nuclear and saturation effects. Our results demonstrate that a future experimental analysis of this process would allow to constraint the QCD dynamics at high energies.

hep-ph↗
arXiv2003

Geometric Scaling in Inclusive Charm Production

We show that the cross section for inclusive charm production exhibits geometric scaling in a large range of photon virtualities. In the HERA kinematic domain the saturation momentum $Q_{sat}^2(x)$ stays below the hard scale $μ_c^2=4m_c^2$, implying charm production probing mostly the color transparency regime and unitarization effects being almost negligible. We derive our results considering two saturation models which are able to describe the DESY ep collider HERA data for the proton structure function at small values of the Bjorken variable $x$. A striking feature is the scaling on $τ=Q_2^2/Q_{sat}^2(x)$ above saturation limit, corroborating recent theoretical studies.

hep-ph↗
arXiv2003

The QCD Pomeron in ultraperipheral heavy ion collisions: III. Photonuclear production of heavy quarks

We calculate the photonuclear production of heavy quarks in ultraperipheral heavy ion collisions. The integrated cross section and the rapidity distribution are computed employing sound high energy QCD formalisms as the collinear and semihard approaches as well as the saturation model. In particular, the color glass condensate (CGC) formalism is also considered using a simple phenomenological parameterization for the color field correlator in the medium, which allow us to obtain more reliable estimates for charm and bottom production at LHC energies.

hep-ph↗
arXiv2003

Dilepton Transverse Momentum in the Color Dipole Approach

We investigate the Drell-Yan transverse momentum distribution in the framework of the color dipole approach. Special attention is paid to parton saturation effects at high energies. Predictions at LHC energies ($\sqrt{s}=14$ TeV) are given and extrapolated down to ISR energies ($\sqrt{s}=62$ GeV). Unitarity corrections are implemented through the multiple scattering Glauber-Mueller approach and are compared with predictions of the BGBK saturation model.

hep-ph↗
arXiv2003

Nuclear Heavy Quark Photoproduction in a Saturation Model

We calculate the nuclear inclusive and diffractive cross sections for heavy quark photoproduction within a phenomenological saturation approach. The nuclear cross section is obtained by the extension of the saturation model through Glauber-Gribov formalism. We predict large nuclear heavy quark cross section at LHC energies.

hep-ph↗
arXiv2003

Deeply Virtual Compton Scattering and Saturation Approach

We investigate the deeply virtual Compton scattering (DVCS) in the color dipole approach, implementing the dipole cross section through the saturation model, which interpolates successfully between soft and hard regimes. The imaginary and real part of the DVCS amplitude are obtained and the results are compared to the available data.

hep-ph↗
arXiv2003

Double meson production in ultraperipheral heavy ion collisions

The double meson production in ultraperipheral heavy ions collisions is addressed, focusing on the particular case of rho-J/Psi 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 rho production cross section using the Pomeron-exchange factorization relations.

hep-ph↗
arXiv2003

Investigating the Drell-Yan transverse momentum distribution in the color dipole approach

We study the influence of unitarity corrections on the Drell-Yan transverse momentum distribution within the color dipole approach. These unitarity corrections are implemented through the multiple scattering Glauber-Mueller approach, which is contrasted with a phenomenological saturation model. The process is analyzed for the center of mass energies of the Relativistic Heavy Ion Collider (RHIC, $\sqrt{s}=500$ GeV) and of the Large Hadron Collider (LHC, $\sqrt{s}=14$ TeV). In addition, the results are extrapolated down to current energies of proton-proton collisions, where non-asymptotic corrections to the dipole approach are needed. It is also shown that in the absence of saturation, the dipole approach can be related to the QCD Compton process.

hep-ph↗
arXiv2003

On a two Pomeron description of the F_2 structure function

We perform a global fit to the inclusive structure function considering a QCD inspired model describing the ep scattering. In lines of a two Pomeron approach, the structure function F_2 has a hard piece given by the model and the remaining soft contributions: the soft Pomeron and non-singlet content. We have investigated several choices for the soft Pomeron and its implication in the data description. In particular, we carefully estimated the relative role of the hard and the soft contributions in a large span of x and Q^2.

hep-ph↗
arXiv2003

The QCD Pomeron in Ultraperipheral Heavy Ion Collisions: II. Heavy Quark Production

The heavy quark production in ultraperipheral heavy ion collisions is investigated, in particular we focus on the results from the coherent interactions given by the two-photon process. One addresses the heavy quark total cross sections at photon level considering the saturation model and the BFKL dynamics in the color dipole picture. The corresponding cross sections at nuclear level are presented. It is verified that the QCD dynamics implies an enhancement of the cross section in comparison with previous calculations.

hep-ph↗
arXiv2003

The QCD Pomeron in Ultraperipheral Heavy Ion Collisions: I. The Double J/Psi Production

The contribution of the QCD Pomeron to the process AA -> AA J/Psi J/Psi is discussed. We focus on the photon-photon collision, with the quasi-real photon coming from the Weizsacker - 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 analyzes of this process can be useful to discriminate the QCD dynamics at high energies.

hep-ph↗
arXiv2002

The QCD gluon ladders and HERA structure function

We report on the extension of the data fitting considering the QCD inspired model based on the summation of gluon ladders applied to the $ep$ scattering. In lines of a two Pomeron approach, the structure function $F_2$ has a hard piece given by the model and the remaining soft contribution: a soft Pomeron and non-singlet content. In this contribution, we carefully estimate the relative role of the hard and the soft pieces from a global fit in a large span of $x$ and $Q^2$.

hep-ph↗
arXiv2002

Heavy Quark Photoproduction in k_T Factorization Approach

We investigate the heavy quark photoproduction based on the k_T factorization approach, focusing on the results from the saturation model. The deviations in the results using the unintegrated gluon distribution considering the saturation model and the derivative of the collinear gluon distribution are analysed. Total cross sections and p_T distributions are analysed in detail, setting the deviations between the color dipole approximation and the complete semihard approach.

hep-ph↗
arXiv2002

Parton saturation effects to the Drell-Yan process in the color dipole picture

We report on the results obtained in the study of the parton saturation effects, taken into account through the multiscattering Glauber-Mueller approach, applied to the Drell-Yan (DY) process described in the color dipole picture. As a main result, one shows that those effects play an important role in the estimates of the DY differential cross section atRHIC energies.

hep-ph↗
arXiv2002

Aspects of the unitarized soft multipomeron approach in DIS and diffraction

We study in detail the main features of the unitarized Regge model (CFKS), recently proposed to describe the small-$Q^2$ domain. It takes into account a two-component description with two types of unitarized contributions: one is the multiple Pomeron exchanges contribution, interacting with the large dipole size configurations, and the other one consists on a unitarized dipole cross section, describing the interaction with the small size dipoles. We compare the resulting dipole cross section to that from the saturation model (GBW).

hep-ph↗
arXiv2002

Describing F_2 through a finite sum of gluon ladders

Electroproduction in deep inelastic scattering at HERA is studied in a model considering a finite sum of gluon ladders, associated with a truncation of the BFKL series. The approach contains the bare two gluon exchange and both one and two rungs contributions. The model is fitted to the data on the inclusive structure function F_2(x,Q^2) in the region x<0.025 and 0.045<Q^2<1500 GeV^2, with a good agreement. Such a description for a large span in Q^2 is obtained through a suitable modeling of the remaining non-perturbative background.

hep-ph↗