arXiv subjects

V. P. Goncalves

Publications and source records attributed to V. P. Goncalves.

172 records · Page 10Linked to original sources

arXiv2002

The High Density Effects in Heavy Quark Production at pA Colliders

In this paper we investigate the role of the high density effects in the heavy quark production cross section in $pA$ processes at RHIC and LHC. We use, as initial condition, a gluon distribution consistent with fixed target nuclear data and the Glauber-Mueller approach to describe the high density effects. We show that this process can be used as a probe of the presence of the high density effects. Moreover, we include these effects in the calculation of the heavy quark production in $AA$ collisions, verifying that they cannot be disregarded both in the estimates of quarkonium suppression and in the initial conditions of the quark-gluon plasma.

hep-ph↗

arXiv2002

Peripheral heavy ion collisions as a probe of the nuclear gluon distribution

At high energies a quark-gluon plasma is expected to be formed in heavy ion collisions at RHIC and LHC. The theoretical description of these processes is directly associated to a complete knowledge of the details of medium effects in the nuclear gluon distribution. In this paper we analyze the possibility to constraint the behavior of this distribution considering peripheral heavy ion collisions. We reanalyze the photoproduction of heavy quarks for the deduction of the in-medium gluon distribution using three current parameterizations for this parton distribution. Moreover, we show that the elastic photoproduction of vector mesons is a potential process to probe the nuclear gluon distribution.

hep-ph↗

arXiv2001

Color Evaporation and Elastic $Υ$ Photoproduction at DESY HERA

The diffractive photoproduction of vector mesons is usually described considering the two-gluon (Pomeron) exchange, non-diagonal parton distributions and the contribution of the real part to the cross section. In this letter we analyze the diffractive photoproduction of the $Υ$ at HERA using an alternative model, the Color Evaporation Model (CEM), where the cross section is simply determined by the boson-gluon cross section and an assumption for the production of the colorless state. We verify that, similarly to the $J/Ψ$ case, the HERA data for this process can be well described by the CEM. Moreover, we propose the analyzes of the ratio $R = σ_Υ / σ_{J/Ψ}$ to discriminate between the distinct approaches.

hep-ph↗

arXiv2001

Hard and Soft Contributions in Diffraction

We report our calculations on the logarithmic slope of the diffractive structure function F_2^D considering distinct approaches coming from both the pQCD and the Regge descriptions of diffractive DIS. Such a quantity is a potential observable to discriminate between pQCD and Regge domains and allows to disentangle the underlying dynamics.

hep-ph↗

arXiv2001

The Logarithmic Slope in Diffractive DIS

The logarithmic slope of diffractive structure function is a potential observable to separate the hard and soft contributions in diffraction, allowing to disentangle the QCD dynamics. In this paper we extend our previous analyzes and calculate the diffractive logarithmic slope for three current approaches in the literature: (i) the Bartels-Wusthoff model, based on perturbative QCD, (ii) the CKMT model, based on Regge theory and (iii) the Golec Biernat - Wusthoff model which assumes that the saturation phenomena is present in the HERA kinematic region. We analyze the transition region of small to large momentum transfer and verify that future experimental results on the diffractive logarithmic slope could discriminate between these approaches.

hep-ph↗

arXiv2001

The Hard and Soft Contributions in Diffraction: A Closer Look

Disentangle the hard and soft dynamics in diffractive DIS is one of the main open questions of the strong interactions. We propose the study of the logarithmic slope in $Q^2$ of the diffractive structure function as a potential observable to discriminate between the Regge and the QCD-based approaches. Our results indicate that a future experimental analyzes could evidentiate the leading dynamics at $ep$ diffractive processes in the HERA kinematical regime.

hep-ph↗

arXiv2001

The Description of $F_2$ at Very High Parton Densities

The behavior of the structure function at high energies (high densities) is directly associated to the gluon distribution. In this paper we analyze the asymptotic behavior of the structure function at very high densities considering a leading and a higher twist relation between these two quantities. We verify that (a) if the leading twist relation between the structure function and the gluon distribution is used, we recover the black disc limit, and (b) a softer behavior is predicted if a higher twist relation between $F_2$ and $xG$ is considered. While the first behavior is well-established by the current high density approaches, the higher twist behavior is a new result. In both cases, the $F_2$ structure function unitarizes and the Froissart boundary is not violated in the asymptotic regime of high density QCD.

hep-ph↗

arXiv2001

The improved nuclear parton distributions

In this paper we propose an improvement of the EKS nuclear parton distributions for the small x region of high energy processes, where the perturbative high parton density effects cannot be disregarded. We analyze the behavior of the ratios $xG_A/xG_N$ and $F_2^A/F_2^D$ and verify that at small x they are strongly modified when compared to the EKS predictions. The implications of our results for the heavy ion collisions in RHIC and LHC are discussed.

hep-ph↗

arXiv2000

Searching Saturation in eA Processes

The high density effects should be manifest at small x and/or large nuclei. In this letter we consider the behavior of nuclear structure function $F_2^A$ slope in the kinematic region which could be explored in the future eA colliders as a search of these effects. We verify that the high density implies that the maximum value of the slope occurs at large values of the photon virtuality, i.e. in a perturbative regime, and is dependent of the number of nucleons A and energy. Our conclusion is that the measurement of this observable will allow to explicit the saturation.

hep-ph↗

arXiv1998

High Density Parton Shadowing Corrections in DIS Scaling Violations

The description of the dynamics at high density parton regime is one of the main open questions of the strong interactions theory. In this paper we address the shadowing corrections (SC) in the scaling violations of the $F_2$ structure function using the eikonal approach. We propose a procedure to estimate the distinct contributions to the SC for $F_2$ and its slope and show that the recent ZEUS data can be described if the SC in the quark and gluon sectors are considered. The radius dependence of the SC is estimated. Moreover, we calculate the superior limit above which the unitarity corrections cannot be disregarded at low $Q^2$ and show that the recent HERA data overcomes this bound.

hep-ph↗