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E. Ferreira

Publications and source records attributed to E. Ferreira.

32 records · Page 2Linked to original sources
arXiv2013

Elastic $\rm{p\bar p}$ Scattering Amplitude at 1.8 TeV and Determination of Total Cross Section

The data on p$\mathrm{\bar p}$ elastic scattering at 1.8 and 1.96 TeV are analysed in terms of real and imaginary amplitudes, in a treatment with high accuracy, covering the whole t-range and satisfying the expectation of dispersion relation for amplitudes and for slopes. A method is introduced for determination of the total cross section and the other forward scattering parameters and to check compatibility of E-710, CDF and the recent D0 data. Slopes $B_R$ and $ B_I$ of the real and imaginary amplitudes, treated as independent quantities, influence the amplitudes in the whole t-range and are important for the determination of the total cross section. The amplitudes are fully constructed, and a prediction is made of a marked dip in $ dσ/dt$ in the $|t|$ range 3 - 5 GeV$^2$ due to the universal contribution of the process of three gluon exchange.

hep-ph↗
arXiv2013

Amplitudes and Observables in pp Elastic Scattering at $\sqrt{s}=7$ TeV

A precise analysis of the pp elastic scattering data at 7 TeV in terms of its amplitudes is performed as an extension of previous studies for lower energies. Slopes $B_{R}$ and $B_{I}$ of the real and imaginary amplitudes are independent quantities, and a proper expression for the Coulomb phase is used. The real and imaginary amplitudes are fully disentangled, consistently with forward dispersion relations for amplitudes and for slopes. We present analytic expressions for the amplitudes that cover all $t$ range completely, while values of total cross section $σ$, ratio $ρ$, $B_{I}$ and $B_{R}$ enter consistently to describe forward scattering. It is stressed that the identification of the amplitudes is an essential step for the description of elastic scattering, and pointed out the importance of the experimental investigation of the transition range from non-perturbative to perturbative dynamics, that may confirm the three gluon exchange mechanism observed at lower energies.

hep-ph↗
arXiv2009

Universality in the Electroproduction of Vector Mesons

We study universality in the electroproduction of vector mesons using a unified nonperturbative approach which has already proved to reproduce extremely well the available experimental data. In this framework, after the extraction of factors that are specific of each vector meson, we arrive at a reduced integrated elastic cross section which is universal. Our calculations suggest a finite infrared behavior for the strong coupling constant.

hep-ph↗
arXiv2009

Nonperturbative and perturbative aspects of photo- and electroproduction of vector mesons

We discuss various aspects of vector meson production, first analysing the interplay between perturbative and nonperturbative aspects of the QCD calculation. Using a general method adapted to incorporate both perturbative and nonpertubative aspects, we show that nonperturbative effects are important for all experimentally available values of the photon virtuality Q2. We compare the huge amount of experimental information now available with our theoretical results obtained using a specific nonperturbative model without free parameters, showing that quite simple features are able to explain the data.

hep-ph↗
arXiv2004

Factorization of the Q^2 dependence in electroproduction of vector mesons

In a framework for nonperturbative QCD calculation of high energy processes, the amplitudes for photo- and electroproduction of vector mesons are written as integrals of the overlap product of photon and vector meson wave functions, multiplied by the amplitude for the scattering of $q\bar{q}$ dipole pairs off the proton. For sizes of the overlap functions that are smaller than the typical ranges of the interaction of the dipoles with the proton, the amplitudes factorize in the form of integrals, here called overlap strengths, formed only with the overlap of the wave functions times the square of the dipole separation. The integration is extended over the light front coordinates describing the $q\bar{q}$ dipoles. With this result, the overlap strengths contain all $Q^2$ dependence of the observables. We show the importance of this factorization in the description of the experimental data for all S-wave vector mesons.

hep-ph↗
arXiv2003

Exclusive electroproduction of J/psi mesons

A nonperturbative calculation of elastic electroproduction of the J/psi meson is presented and compared to the experimental data. Our model describes well the observed dependences of the cross sections on the photon virtuality Q2 and on the energy, and the measured ratio R of longitudinal to transverse cross sections.

hep-ph↗
arXiv2002

Nonperturbative QCD treatment of $J/ψ$ photoproduction

We present a nonperturbative QCD calculation of elastic $J/ψ$ meson production in photon-proton scattering at high energies. Using light cone wave functions of the photon and vector mesons, and the framework of the model of the stochastic QCD vacuum, we calculate the differential and integrated elastic cross sections for $γp \goto J/ψp $ . With an energy dependence following the two-pomeron model we are able to give a consistent description of the integrated cross sections and the differential cross sections at low $|t|$ in the range from 20 GeV up to the highest HERA energies. We discuss different approaches to introduce saturation and find no specific effects up to energies presently available. We also calculate and compare to experiments the cross section for $\upsilon$ photoproduction.

hep-ph↗
arXiv2001

Screening Corrections in Photo and DIS Production of $J/Ψ$

Photo and DIS production of $J/Ψ$ are investigated and compared with calculations based on pQCD in the LLA approximation without and with screening corrections. The calculation includes corrections induced by the real part of the production amplitude, the skewed (off diagonal) gluon structure function and the relativistic Fermi motion within the charmonium system. Our pQCD results are also compared with the predictions obtained from a Regge type two Pomeron model. Our results suggest some preference for our screened model, but the available data does not enable us to exclude any of the three models we have examined. The properties of these models, when extrapolated to both low and very high energies may provide a more effective discrimination between the different parameterizations.

hep-ph↗
arXiv2000

Scaling Violations in the $Q^2$ Logarithmic Derivative of $F_2$

We examine the latest HERA experimental measurements of the $Q^2$ logarithmic derivative of the proton structure function. We analyze the characteristics of DGLAP with and without screening, as well as a Regge type model, and compare their predictions to all available data on $\slope$ including those for fixed W. Our results show that the present data can be described in pQCD taking into account shadowing corrections. However, such a description cannot be considered a conclusive signal of gluon saturation since the experimental data on $\slope$ do not allow one to discriminate between the various approaches, in spite of their very different construction.

hep-ph↗
arXiv2000

Screening corrections in DIS at low Q^2 and x

In this investigation we present a detailed study of $\partial F_2/\partial \ln Q^2$ which is supported by a coupled analysis of $J/Ψ$ photo and DIS production. Both channels are directly proportional to $xG(x,Q^2)$, and as such serve as excellent discriminators between different approaches and models. We then show that taking GRV98NLO as input and correcting it for SC, we can reproduce the recent HERA data well. The calculation depends on one parameter $R^2=8.5GeV^{-2}$ which is directly determined from the $J/Ψ$ photoproduction forward differential slope. With this input we obtain an excellent fit to the $J/Ψ$ photo and DIS production data. Our calculations made in the LLA of pQCD take into account the corrections implied by the real part of the production amplitude, off diagonal (skewed) gluon distributions and the Fermi motion of the charm quarks within the bound Charmonium system.

hep-ph↗
arXiv1999

Form Factors and Decay Rates for Heavy $Λ$ Semileptonic Decays from QCD Sum Rules

QCD sum rules for the determination of form factors of $Λ_b$ and $Λ_c$ semileptonic decays are investigated. With a form for the baryonic current appropriate for the limits of the heavy quark symmetries, the different tensor structures occurring in the two- and three-point functions are separately studied, and in each case general relations are written for the form factors. Particular attention is given to the treatment of the kinematical region ascribed to the continuum. The $t$-dependence of the form factors and the decay rates are numerically evaluated and compared to experimental information.

hep-ph↗
arXiv1998

QCD Sum Rules Calculation of Heavy $Λ$ Semileptonic Decay

We set up sum rules for heavy lambda decays in a full QCD calculation which in the heavy quark mass limit incorporates the symmetries of heavy quark effective theory. For the semileptonic $\La_c$ decay we obtain a reasonable agreement with experiment. For the $\La_b$ semileptonic decay we find at the zero recoil point a violation of the heavy quark symmetry of about 20%.

hep-ph↗