Vector Dominance Model Research Articles

Generalised vector dominance: Off-diagonal terms and asymptotic SU(4)

Asymptotic SU(4) symmetry is imposed on generalised vector dominance models with off-diagonal terms, relating the magnitudes of these terms in the various sectors V = ϱ, ω, φ, ψ. While the structure functions are modified, their ratios remain similar to those of the diagonal model. Strangeness and charm production are suppressed for low Q 2 < M φ 2, M ψ 2 respectively.

ω Meson photoproduction from deuterium at 3.9 GeV photon energy

Measurements are presented of the cross sections for ω meson photoproduction from deuterium at an average photon energy of 3.9 GeV. The cross section for the coherent process γd → d ω is found to be 1.4 ± 0.5 μb and that for the incoherent process γd → np ω is 3.3 ± 0.7 μb. The forward differential cross section for γd → d ω is estimated to be (d σ/d t) t=0 = 54 ± 20 μb/GeV 2. This result indicates that the value of the A 2 exchange amplitude in ω photoproduction from hydrogen is less than that predicted from the measurements of the difference between the total hadron photoproduction cross sections from neutrons and protons. We note that the world data tend to show that the A 2 exchange amplitude is more consistent with zero than with the value needed to explain these differences. Measurements are also presented of the ratio of the coupling constants of the photon to the ϱ and ω mesons which tend to favour the vector dominance model proposed by Das, Mathur and Okubo with exact SU(3) symmetry at infinite energies.

Largexdependence ofνW2in the generalized vector-dominance model

It is well known that the usual generalized vector-meson-dominance (GVMD) model gives too large a contribution to $\ensuremath{\nu}{W}_{2}$ for large $x$. Various heuristic modifications, for example making use of the ${t}_{min}$ effect, have been proposed in order to achieve a reduction of this contribution. In this paper we examine within the GVMD context whether such reductions can rigorously be achieved. This is done utilizing a potential as well as a relativistic eikonal model. We find that whereas a reduction equivalent to that of ${t}_{min}$ can be arranged in vector-meson photoproduction, the same is not true for virtual-photon Compton scattering in such diagonal models. The reason for this difference is discussed in detail. Finally we show that the desired reduction can be obtained if nondiagonal vector-meson scattering terms are properly taken into account.

Vector-meson radiative decays and SU(3)

Recently measured radiative decay rates for vector mesons, when compared with SU(3) and quark-model predictions, are known to disagree by factors of 2 or 3. Some simple SU(3) -breaking mechanisms in the framework of the vector-dominance model are considered, but none can fit all the data with ''reasonable'' parameters. It is concluded that either the new data from Primakoff-effect experiments have larger uncertainties than quoted or the usual ideas of SU(3) -invariant three-particle vertices with U-spin invariance for photon couplings are not valid. (AIP)

Interpretation of energy dependence of forwardψ(3.1)photoproduction

Several $\ensuremath{\psi}$ photoproduction measurements are analyzed within the framework of the vector-dominance model. The $\ensuremath{\psi}$-nucleon inelastic cross section is obtained as a function of energy. It shows behavior consistent with a threshold corresponding to the reaction $\ensuremath{\psi}N\ensuremath{\rightarrow}D\overline{D}N$.

Shadowing in nuclear photoabsorption

Shadowing in nuclear photoabsorption is studied using a generalised vector dominance model, and the simplifying assumptions of previous calculations shown to be inadequate. Less shadowing is found than hitherto, with possible anti-shadowing indicated for x′ ≳ 0.07. The results are compatible with experiment within the substantial systematic errors.

Scaling in e +e − annihilation and the quark binding potential

Within the framework of the generalized vector dominance model, the leptonic widths of the new vector mesons are used to extract information about the quark binding potential. We arrive at conclusions similar to those of other models, based on the charmonium picture. A fit to R = σ(e −e + → hadrons)/ σ(e +e − → ω + ω − is given.

Hadron production in photon-photon collisions

We analyze deep-inelastic photon-photon collisions via the two-photon mechanism in electron-positron (-electron) colliding beams in a form especially suitable for experimental analysis. It is shown that by a helicity analysis similar to that used in electroproduction experiments, we can separate five of the eight structure functions describing the process ${\ensuremath{\gamma}}^{*}+{\ensuremath{\gamma}}^{*}\ensuremath{\rightarrow}\mathrm{hadrons}$. The helicity cross sections for this process and for the process with one real photon (inelastic electron-photon scattering) are related to structure functions, and are evaluated using quark light-cone algebra. There are anomalous contributions to the structure functions for the inelastic electron-photon scattering which arise both in parton as well as generalized vector-meson-dominance models. This suggests a connection between these two types of models for photon-photon scattering. Further, we use vector-meson dominance to construct a sum rule for ${\ensuremath{\sigma}}_{\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}\mathrm{hadrons}}$ from which it is estimated that roughly 20% of the cross section should be built up from higher-mass vector states. Using a spectral representation for the total transverse cross section, and the "aligned-jet" vector-dominance model we achieve a connection, via a "correspondence principle," with the parton model for the hadron multiplicities in photon-photon collisions. We also comment on inclusive pion multiplicities and the approach to scaling for photon-photon processes in the light-cone algebra.

Off-diagonal generalized vector dominance: A comparison with recentepdeep-inelastic data

The predictions of a recently suggested generalized vector-dominance model which includes off-diagonal terms are compared with 4° deep-inelastic ep scattering data.Received 22 December 1975DOI:https://doi.org/10.1103/PhysRevD.14.93©1976 American Physical Society

Generalized vector-dominance model for lepton production at large transverse momenta

The direct production of leptons at large transverse momentap⊥ is studied in the framework of generalized vector dominance (GVD). A simple model is constructed for inclusive vector-meson production that accounts for all available data at large and smallp⊥. The muon-pair distributions as functions of the muon-pair mass are calculated in fair agreement with experiment. It is shown that the old vector mesons ρ, ω, ϕ together with their GVD partners and the new particles ψ, ψ′ can account for all the observed large-p⊥ lepton yields.

SU 3, quark model and VDM solutions for the radiative-transition problem

The recent failures of the quark model and the vector-dominance model to explain the radiative transitions V → P + γ are analysed. Within the quark model several partial solutions exhibiting the octet dominance for the electromagnetic current are noticed. A genuineSU3 solution is also proposed relying on theω-ϕ current mixing. The VDM difficulties seem to be solvable only by introducing higher vector mesons.

Generalized vector-dominance model of dilepton production

We construct a model for dilepton production in hadron-hadron interactions based on the idea of generalized vector dominance. We argue that in the high-mass region the generalized vector-dominance model and the Drell-Yan parton model are alternative descriptions of the same underlying physics. In the low-mass regions the models differ; the vector-dominance approach predicts a greater production of dileptons. We compare the model to the limited dilepton data that are presently available and also integrate over one of the leptons to study the contributions to the single-lepton yield. We find that the high-mass vector mesons which are the hallmark of the generalized vector-dominance model make little contribution to the large yield of leptons observed in the transverse-momentum range $1&lt;{p}_{\ensuremath{\perp}}&lt;6$ GeV. We illustrate with a simple model, however, the extreme sensitivity of the large-${p}_{\ensuremath{\perp}}$ lepton yield to the large-transverse-momentum tail of vector-meson production.

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.

Dimuon data test weak current models

Dimuon events in neutrino scattering probably signal the production of new quantum numbers, generically termed charm, and directly probe the charm-changing weak current. We show that available x- and y-distributions already test weak-current models stringently. The four-quark model agrees with data. Vectorlike six-quark theories agree only if some of the new quantum numbers are not yet excited. Charmed quarks with charge − 4 3 give disagreement. Vector dominance models are unsatisfactory.

Vector–vector–pseudoscalar couplings, radiative decays, and possible existence of ψ-like pseudoscalar mesons

Possible interactions of the ψ particles are analyzed with emphasis on vector–vector–pseudoscalar couplings. Radiative decays are studied in some detail in the context of the vector dominance model. The possibility that there might exist ψ-like pseudoscalar mesons which couple strongly to the ψ's is examined. The relevance of our phenomenological analysis to the charm and color scheme interpretations of the new particle is discussed.

New shadowing corrections to photon-deuteron total cross sections

The Glauber correction to photon-deuteron total cross sections is reexamined in the light of the Extended Vector Dominance Model. If the photon couples to an infinite number of π-like vector mesons one obtains an extra shadowing correction of about 3 μb at high energy. Some of the consequences of this new contribution are briefly discussed.

Photoproduction of ψ(3100), geometrical scaling and the quark model

Photoproduction of ψ(3100) is described combining the vector dominance model and the quark model with a particular geometrical scaling hypothesis implying SU 4 to be an exact symmetry at infinite energies.

The ϱNN vertex in vector-dominance models

A new πN amplitude analysis and experimental data for the pion form factor have been used in order to determine the I = J = 1 ππ N N partial waves and properties of the ϱNN vertices. The results are compared with earlier determinations of ϱNN coupling constants from πN and NN scattering and from nucleon for, factor data.

Parton model and deep inelastic scattering on nuclei

The parton model is shown to predict antishadowing phenomenon in deep inelastic scattering of electrons or neutrinos off a nucleus. The antishadowing is expected to take place for intermediate values of scaling variable x, x ≈ x 0 ≈ 0.05 – 0.1, linking the regions of diffraction and incoherent scattering. This effect could account for the experimentally observed lack of shadowing as compared with the predictions of the vector dominance model. The sum rule is proposed according to which the integrated cross section foe electron-nucleus interaction is equal to the sum cross sections for electron-nucleon interactions.

Some information from nucleon-antinucleon annihilation at rest: e +e − annihilation, hadronic fragmentation and deep inelastic structure functions

The experimental spectra of charged pions in NN annihilation at rest are described in a model of quasi-two-body decays. The same model predicts the π 0, ϱ and ω spectra. We apply a previous calculation to determine in the vector-dominance model, the pions spectra in e +e − annihilation at the same energy. The NN system is then used as a heavy hadron in order to describe, in a model-independent way: (i) the projectile fragmentation part in inclusive reactions; (ii) the valence part of the deep inelastic structure function.