Generalized Vector Meson Dominance Model Research Articles

Upsilon Photo-Production off Proton in QCD Inspired Model

Based on the generalized vector meson dominance model in QCD, we study photoproduction of vector meson γ off the proton by use of the QCD inspired model in which the contributions from quark-quark, gluon-gluon, and quark-gluon interference term to observable are taken into consideration. Calculations are performed for total cross section σtot, differential cross section dσ/dt, ratio of the real part to imaginary part of forward scattering amplitude ρ, and nuclear slop parameter function β. The mediators of interactions between projectiles (the quark and antiquark pair fluctuated from the real the photon) and the proton target (three-quark system) are the tensor Glueball and Odderon instead of using the usual Pomeron exchange. The theoretical predictions for σtot (s) are consistent with the experimental data within error bars of the data. The data for dσ/dt, ρ, and β are urgently needed.

Diffractive upsilon photo-production off the proton in the QCD inspired model

Based on the generalized vector meson dominance model in QCD, we study the photoproduction of vector meson ϒ off the proton by use of the QCD-inspired model in which the contributions from quark-quark, gluon-gluon and quark-gluon interference term to observable are taken into consideration. Calculations are performed for total cross section σ tot, differential cross section dσ/dt, ratio of the real part to imaginary part of forward scattering amplitude ρ and nuclear slop parameter function β. We analyze the individual contributions from quark gluon degrees of freedom and the QCD Odderon to the total cross section σ tot (s), differential cross section dσ/dt, ratio of the real part to imaginary part of the forward scattering amplitude ρ, and nuclear slop parameter function β. The mediators of interactions between projectiles (the quark and antiquark pair fluctuated from the real photon) and the proton target (three quark system) are the tensor Glueball and Odderon instead of using the usual Pomeron exchange. The theoretical predictions for σ tot(s) are consistent with the experimental data within error bars of the data. The data for dσ/dt, β and ρ are urgently needed. The gluon-gluon interaction makes a significant contribution to the observables while the Odderon contribution is negligibly small. Therefore, we may conclude that it is impossible to find the QCD Odderon in the γ+p → ϒ+p process as suggested before.

Deeply Virtual Compton Scattering on nucleons and nuclei in the Generalized Vector Meson Dominance model

We consider Deeply Virtual Compton Scattering (DVCS) on nucleons and nuclei in the framework of the Generalized Vector Meson Dominance (GVMD) model. We demonstrate that the GVMD model provides a good description of the HERA data on the dependence of the proton DVCS cross-section on Q2, W (at Q 2 = 4 GeV^2) and t . At Q 2 = 8 GeV^2, the soft W -behavior of the GVMD model somewhat underestimates the W -dependence of the DVCS cross-section due to the hard contribution not present in the GVMD model. We estimate 1/Q 2 power-suppressed corrections to the DVCS amplitude and the DVCS cross-section and find them large. We also make predictions for the nuclear DVCS amplitude and cross-section in the kinematics of the future Electron-Ion Collider. We predict significant nuclear shadowing, which matches well predictions of the leading-twist nuclear shadowing in DIS on nuclei.

Charm production in antiproton–nucleus collisions at the [formula omitted] and the [formula omitted] thresholds

We discuss the production of charmonium states in antiproton–nucleus collisions at the ψ′ threshold. It is explained that measurements in p¯A collisions will allow to get new information about the strengths of the inelastic J/ψN and ψ′N interaction, on the production of Λc and D¯ in charmonium–nucleon interactions and for the first time about the nondiagonal transitions ψ′N→J/ψN. The inelastic J/ψ-nucleon cross section is extracted from the comparison of hadron–nucleus collisions with hadron–nucleon collisions. We extract the total J/ψ-nucleon cross section from photon–nucleon collisions by accounting for the color transparency phenomenon within the frame of the GVDM (generalized vector meson dominance model). We evaluate within the GVDM the inelastic ψ′-nucleon cross section as well as the cross section for the nondiagonal transitions. Predictions for the ratio of J/ψ to ψ′ yields in antiproton–nucleus scatterings close to the threshold of ψ′ production for different nuclear targets are presented.

Spin structure function g 1 (x, Q) and the DHGHY integral I(Q) at low Q: predictions from the GVMD model

Theoretical predictions for polarized nucleon structure function $g_1(x,Q^2)$ at low $Q^2$ are obtained in the framework of the Generalized Vector Meson Dominance model. Contributions from both light and heavy vector mesons are evaluated. In the photoproduction limit the first moment of $g_1$ is related to the static properties of nucleon via the Drell-Hearn-Gerasimov-Hosoda-Yamamoto sum rule. This property is employed to fix the magnitude of the light vector meson contribution to $g_1$, using the recent measurements in the region of baryonic resonances. Results are compared to the data on $g_1(x,Q^2)$. Finally, the DHGHY moment function $I(Q^2)$ is calculated, and our theoretical predictions are confronted with the recent preliminary data obtained at the Jefferson Laboratory.

Study of the processe+e−→π+π−π0in the energy regionsfrom 0.98 to 1.38 GeV

The cross section of the process $e^+e^-\to \pi^+\pi^-\pi^0$ was measured in the Spherical Neutral Detector experiment at the VEPP-2M collider in the energy region $\sqrt[]{s} = 980 \div 1380$ MeV. The measured cross section, together with the $e^+e^-\to \pi^+\pi^-\pi^0$ and $\omega\pi^+\pi^-$ cross sections obtained in other experiments, was analyzed in the framework of the generalized vector meson dominance model. It was found that the experimental data can be described by a sum of $\omega$, $\phi$ mesons and two $\omega^\prime$ and $\omega^{\prime\prime}$ resonances contributions, with masses $m_{\omega^\prime}\sim 1490$,$m_{\omega^{\prime\prime}}\sim 1790$ MeV and widths $\Gamma_{\omega^\prime}\sim 1210$, $\Gamma_{\omega^{\prime\prime}}\sim 560$ MeV. The analysis of the $\pi^+\pi^-$ invariant mass spectra in the energy region $\sqrt[]{s}$ from 1100 to 1380 MeV has shown that for their descriptionone should take into account the $e^+e^-\to\omega\pi^0\to\pi^+\pi^-\pi^0$ mechanism also. The phase between the amplitudes corresponding to the $e^+e^-\to\omega\pi$ and $e^+e^-\to\rho\pi$ intermediate states was measured for the first time. The value of the phase is close to zero and depends on energy.

Gluon versus sea quark shadowing

We calculate the shadowing of sea quarks and gluons and show that the shadowing of gluons is not simply given by the sea quark shadowing, especially at small x. The calculations are done in the lab frame approach by using the generalized vector meson dominance model. Here the virtual photon turns into a hadronic fluctuation long before the nucleus. The subsequent coherent interaction with more than one nucleon in the nucleus leads to the depletion σ(γ ∗A)<Aσ(γ ∗N) known as shadowing. A comparison of the shadowing of quarks to E665 data for 40 Ca and 207 Pb shows good agreement.

Cross section fluctuations of a photon projectile in the generalized vector meson dominance model

We explain that the generalized vector meson dominance (GVMD) models successful in the theoretical description of photoproduction and electroproduction in high energy processes effectively implement color coherent phenomena expected in QCD. Within a model, which reproduces Bjorken scaling and nuclear shadowing for deep inelastic processes, we calculate ${P}_{\ensuremath{\gamma}}(\ensuremath{\sigma}{,Q}^{2}),$ the probability for a photon to interact with a target with the cross section \ensuremath{\sigma}. We find that within the GVMD model the virtual photon has two main components: the ``hard'' one with a small cross section of the order of ${1/Q}^{2}$ and the high probability and the ``soft'' one with a typical hadronic cross section with the probability suppressed by the factor of ${1/Q}^{2}.$ Thus the GVDM model produces ${P}_{\ensuremath{\gamma}}(\ensuremath{\sigma}{,Q}^{2})$ similar to that within the parton model and suggests the interplay between hard and soft QCD at ${Q}^{2}&gt;1{\mathrm{GeV}}^{2}.$ We study the limit $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\sigma}}0$ and show that ${P}_{\ensuremath{\gamma}}(\ensuremath{\sigma}{,Q}^{2})\ensuremath{\propto}1/\ensuremath{\sigma}$ in both the GVMD model and QCD. Thus similarly to the parton model the GVMD model predicts the color transparency phenomenon. This is an indirect indication that Bjorken scaling, color transparency and shadowing in nuclei in DIS are closely related.

$q\bar q$ PAIRS IN THE GENERALIZED VECTOR MESON DOMINANCE MODEL FOR THE NUCLEAR SHADOWING EFFECT IN DEEP INELASTIC SCATTERING

The [Formula: see text] pair component of the virtual photon in deep inelastic scattering is considered in the context of the generalized vector meson dominance model in order to explain the shadowing effect within the conventional nuclear model. The [Formula: see text]-nucleon interaction is estimated by the additive quark model. The nuclear effect is taken into account by the detailed evaluation of the microscopic passage of both hardonic and electromagnetic components of the virtual photon through the nuclear medium. Good predictions of the structure function ratio are obtained from the shadowing region to the usual EMC effect in terms of the conventional nuclear model, but the finer target dependence in the shadowing region is not obtained.

TheN-? transition form factor and anomalous?-decays into octet-decuplet baryon-antibaryon Pairs

We develop a Generalized-Vector-Meson Dominance Model (GVDM) for the invariantN-Δ transition form factors which incorporates the correct largeq2 power behaviour of QCD and describes the available lowq2 space-like data. We then use this GVDM transition form factor in the time-like region to calculate theSU (3) singlet and octet contributions to Ψ-decays into octet-decuplet baryon-antibaryon pairs. The results are compared to recent data on Ψ-decays into octet-decuplet baryon-antibaryon pairs.

Sum rules for vector-meson-nucleon scattering from the generalized vector-meson dominance model

The generalized vector-meson dominance model (GVD) yields very satisfactory predictions for total cross-sections of the processes e+e--> hadrons and V3W-+ hadrons, for the structure function W2(v, q2) in deep inelastic e3W scattering and for the photoproduction of vector mesons on nucleons. For results and references see e.g. ref. (1.s). As yet no significant contradiction with experiment has been reported. The price to pay, however, is that it is necessary to make guesses about the scattering of higher vector mesons and nucleons. To be sure, this information can be obtained from highenergy photoproduction on nuclei, but at present i t is not available and guess work is necessary. In view of the successes of the GVD model, it seems justified to invert the usual procedure and to use the data from photon interactions and the model to learn about vector-meson-nucleon scattering. As a byproduct, we should be able to understand why realizations of GVD, which make widely different assumptions about vectormeson-nucleon scattering (compare e.g. ref. (1,~)), succeed in reproducing the same experimental data. Following the usual practice, we assume that the vector mesons can be arranged into recurrences, with the squared mass of the n-th vector meson from recurrence v given by

Shadowing in photon-nucleus scattering and the two-component model

A recently proposed two-component model for deep-inelastic electroproduction, in which the generalized-vector-meson-dominance (GVMD) component was augmented by a component due to direct photon interaction with the valence quarks, is applied to the study of photon shadowing in nuclei. We calculate the effective number of nucleons (${A}_{\mathrm{eff}}$) as a function of the photon energy for various values of $\ensuremath{-}{q}^{2}$ and several nuclei in a GVMD model. The resulting photon-nucleus cross section as a function of energy is consistent with the data and the $\ensuremath{\rho}$-nucleon cross section is in agreement with expectations. The results for ${A}_{\mathrm{eff}}$ are in satisfactory agreement with experiment and represent an improvement of the pure GVMD result.

Direct lepton production in the generalized vector-dominance model

The direct production of leptons at large transverse momenta is studied in the generalized vector-meson-dominance model (GVDM). It is concluded that the known vector mesons (old and new) together with their GVDM partners may account for all the observed leptons.

High Energy Photo-Reactions and Generalized Vector Meson Dominance Model in the Relativistically Extended Quark Model

High Energy Photo-Reactions and Generalized Vector Meson Dominance Model in the Relativistically Extended Quark Model