Vector Meson Dominance Research Articles

Measurement of the e + e – → ηπ+π– cross section in the center-of-mass energy range 1.22–2.00 GeV with the SND detector at the VEPP-2000 collider

In the experiment with the SND detector at the VEPP-2000 e+e– collider the cross section for the process e+e– → ηπ+π– has been measured in the center-of-mass energy range from 1.22 to 2.00 GeV. Obtained results are in agreement with previous measurements and have better accuracy. The energy dependence of the e+e– → ηπ+π– cross section has been fitted with the vector-meson dominance model. From this fit the product of the branching fractions B(ρ(1450) → ηπ+π–)B(ρ(1450) → π+π–) has been extracted and compared with the same products for (ρ(1450) → ωП0 and (ρ(1450) → π+π– decays. The obtained cross section data have been also used to test the conservation of vector current hypothesis.

Nuclear shadowing in photoproduction of ρ mesons in ultraperipheral nucleus collisions at RHIC and the LHC

We argue that with an increase of the collision energy, elastic photoproduction of ρ mesons on nuclei becomes affected by the significant cross section of photon inelastic diffraction into large masses, which results in the sizable inelastic nuclear shadowing correction to σγA→ρA and the reduced effective ρ-nucleon cross section. We take these effects into account by combining the vector meson dominance model, which we upgrade to include the contribution of high-mass fluctuations of the photon according to QCD constraints, and the Gribov–Glauber approximation for nuclear shadowing, where the inelastic nuclear shadowing is included by means of cross section fluctuations. The resulting approach allows us to successfully describe the data on elastic ρ photoproduction on nuclei in heavy ion UPCs in the 7 GeV<Wγp<46 GeV energy range and to predict the value of the cross section of coherent ρ photoproduction in Pb–Pb UPCs at sNN=5.02 TeV in Run 2 at the LHC, dσPbPb→ρPbPb(y=0)/dy=560±25 mb.

Photon structure functions at small x in holographic QCD

We investigate the photon structure functions at small Bjorken variable x in the framework of the holographic QCD, assuming dominance of the Pomeron exchange. The quasi-real photon structure functions are expressed as convolution of the Brower–Polchinski–Strassler–Tan (BPST) Pomeron kernel and the known wave functions of the U(1) vector field in the five-dimensional AdS space, in which the involved parameters in the BPST kernel have been fixed in previous studies of the nucleon structure functions. The predicted photon structure functions, as confronted with data, provide a clean test of the BPST kernel. The agreement between theoretical predictions and data is demonstrated, which supports applications of holographic QCD to hadronic processes in the nonperturbative region. Our results are also consistent with those derived from the parton distribution functions of the photon proposed by Glück, Reya, and Schienbein, implying realization of the vector meson dominance in the present model setup.

Vacuum structure of vector mesons in QCD

We study the chiral dynamics of vector mesons in two-flavor QCD in vacuum by utilizing a functional renormalization group approach. This allows us to capture the dynamical transition from the quark-gluon phase at high energies to the hadronic phase at low energies without the necessity of model parameter tuning. We use this to analyze the scaling of vector meson masses towards the chiral symmetry breaking scale, the decoupling of the mesons at high energies and the validity of vector meson dominance.

Nucleon spin structure

This paper contains three parts relating to the nucleon spin structure in a simple picture of the nucleon: (i) The polarized gluon distribution in the proton is dynamically predicted starting from a low scale by using a nonlinear quantum chromodynamics (QCD) evolution equation — the Dokshitzer–Gribov–Lipatov–Altarelli–Paris (DGLAP) equation with the parton recombination corrections, where the nucleon is almost consisted only of valence quarks. We find that the contribution of the gluon polarization to the nucleon spin structure is much larger than the predictions of most other theories. This result suggests that a significant orbital angular momentum of the gluons is required to balance the gluon spin momentum. (ii) The spin structure function [Formula: see text] of the proton is studied, where the perturbative evolution of parton distributions and nonperturbative vector meson dominance (VMD) model are used. We predict [Formula: see text] asymptotic behavior at small x from lower Q2to higher Q2. The results are compatible with the data including the early HERA estimations and COMPASS new results. (iii) The generalized Gerasimov–Drell–Hearn (GDH) sum rule is understood based on the polarized parton distributions of the proton with the higher twist contributions. A simple parameterized formula is proposed to clearly present the contributions of different components in the proton to [Formula: see text]. The results suggest a possible extended objects with size 0.2–0.3 fm inside the proton.

Determining the magnetic dipole moment of the rho meson

We elaborate on the procedure followed to determine the magnetic dipole moment of the rho meson, μp = 2.1 ± 0.5[e/2mρ], from the e+e- → π+π-2π0 process. Using preliminary data from the BaBar Collaboration and a vector meson dominance approach.

Photoproduction of the f2(1270) resonance

We have performed a calculation of the $\gamma p \to \pi^+ \pi^- p$ reaction, where the two pions have been separated in $D$-wave producing the $f_2(1270)$ resonance. We use elements of the local hidden gauge approach that provides the interaction of vector mesons in which the $f_2(1270)$ resonance appears as a $\rho$-$\rho$ molecular state in $L=0$ and spin 2. The vector meson dominance, incorporated in the local hidden gauge approach converts a photon into a $\rho^0$ meson and the other meson connects the photon with the proton. The picture is simple and has no free parameters, since the parameters of the theory have been constrained in the previous study of the vector-vector states. In a second step we introduce new elements, not present in the local hidden gauge approach, adapting the $\rho$ propagator to Regge phenomenology and introducing the $\rho NN$ tensor coupling. We find that both the differential cross section as well as the $t$ dependence of the cross section are in good agreement with the experimental results and provide support for the molecular picture of the $f_2(1270)$ in the first baryonic reaction where it has been tested.

Describing radiation decay using the instant form of relativistic quantum mechanics

For a transition between states with different total angular momentum values, we develop a method for constructing an electromagnetic current operator that satisfies the Lorentz-covariance and current-conservation conditions. Our method is realized in the framework of an instant form of relativistic quantum mechanics using the general method of relativistic parameterization of matrix elements of local operators. We illustrate the method by calculating the radiation decay of a ρ-meson into a pion. In the modified impulse approximation, we obtain an analytic expression for the transition form factor of this process in the form of an integral representation of dispersion type. Results of the numerical calculation agree with the results of calculating the light-front dynamics and with the model of vector meson dominance.

Determination of the magnetic dipole moment of the rho meson using four-pion electroproduction data

We determine the magnetic dipole moment of the rho meson using preliminary data from the BaBar Collaboration for the [Formula: see text] process, in the center of mass energy range from 0.9 to 2.2 GeV. We describe the [Formula: see text] vertex using a vector meson dominance model, including the intermediate resonance contributions relevant at these energies. We find that [Formula: see text] in [Formula: see text] units.

Observation of the Dalitz decayη′→γe+e−

We report the first observation of the Dalitz decay $\eta' \to \gamma e^+e^-$, based on a data sample of 1.31 billion $J/\psi$ events collected with the BESIII detector. The $\eta'$ mesons are produced via the $J/\psi \to \gamma \eta'$ decay process. The ratio $\Gamma(\eta' \to \gamma e^+ e^-)/\Gamma(\eta'\to\gamma\gamma)$ is measured to be $(2.13\pm0.09(\text{stat.})\pm0.07(\text{sys.}))\times10^{-2}$. This corresponds to a branching fraction ${\cal B}(\eta' \to \gamma e^+e^-)= (4.69 \pm0.20(\text{stat.})\pm0.23(\text{sys.}))\times10^{-4}$. The transition form factor is extracted and different expressions are compared to the measured dependence on the $e^+e^-$ invariant mass. The results are consistent with the prediction of the Vector Meson Dominance model.

Ward identities, B → V transition form factors and applications

Long distance effects are studied in the rare exclusive semileptonic B(d,s) → Vℓ+ℓ− decays, where V denotes a K* or ϕ meson. The form factors, which describe the meson transition amplitudes in the effective Hamiltonian approach, are calculated by means of Ward identities, experimental constraints and extrapolated within a general vector meson dominance framework. These form factors are then compared to the ones obtained in Lattice QCD simulations, with Light Cone Sum Rules and a Dyson-Schwinger equation approach. Additionally, the Bd → K*ℓ+ℓ− and Bs → ϕℓ+ℓ− branching ratios are computed and the differential branching fractions are given as a function of the squared-momentum transfer.

Analysis of the strong coupling constant $$G_{D_{s}^{*}D_{s}\phi }$$ G D s ∗ D s ϕ and the decay width of $$D_{s}^{*}\rightarrow D_{s}\gamma $$ D s ∗ → D s γ with QCD sum rules

In this article, we calculate the form factors and the coupling constant of the vertex $D_{s}^{*}D_{s}\phi$ using the three-point QCD sum rules. We consider the contributions of the vacuum condensates up to dimension $7$ in the operator product expansion(OPE). And all possible off-shell cases are considered, $\phi$, $D_{s}$ and $D_{s}^{*}$, resulting in three different form factors. Then we fit the form factors into analytical functions and extrapolate them into time-like regions, which giving the coupling constant for the process. Our analysis indicates that the coupling constant for this vertex is $G_{Ds*Ds\phi}=4.12\pm0.70 GeV^{-1}$. The results of this work are very useful in the other phenomenological analysis. As an application, we calculate the coupling constant for the decay channel $D_{s}^{*}\rightarrow D_{s}\gamma$ and analyze the width of this decay with the assumption of the vector meson dominance of the intermediate $\phi(1020)$. Our final result about the decay width of this decay channel is $\Gamma=0.59\pm0.15keV$.

Measurement of thee+e−→ηπ+π−cross section in the center-of-mass energy range 1.22–2.00 GeV with the SND detector at the VEPP-2000 collider

In the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider the cross section for the process $e^+e^-\to\eta\pi^+\pi^-$ has been measured in the center-of-mass energy range from 1.22 to 2.00 GeV. Obtained results are in agreement with previous measurements and have better accuracy. The energy dependence of the $e^+e^-\to\eta\pi^+\pi^-$ cross section has been fitted with the vector-meson dominance model. From this fit the product of the branching fractions $B(\rho(1450)\to\eta\pi^+\pi^-)B(\rho(1450)\to e^+e^-)$ has been extracted and compared with the same products for $\rho(1450)\to\omega\pi^0$ and $\rho(1450)\to\pi^+\pi^-$ decays. The obtained cross section data have been also used to test the conservation of vector current hypothesis.

Equivalence Between Vector Meson Dominance and Unitarised Chiral Perturbation Theory

It is explicitly shown that either the approximate solution of the integral equation for the inverse of the pion form facto,r or the result of the Pad\(\text{\'e}\) approximant method of resumming the one loop Chiral Perturbation Theory (CPTH) are equivalent to the standard vector meson dominance (VMD) models, using the vector meson coupling to two pseudoscalars given by the KSRF relation. Inconsistencies between the one loop CPTH and its unitarised version (or the VMD model) are pointed out. The situation is better for the CPTH calculation of the scalar form factor and the related S-wave $\pi \pi$ scattering. The branching ratios of \(\tau \to \pi^+ \pi^0 \nu \), \(\tau \to K \pi \nu \), \(\tau \to K^+ \eta \nu\) and $\tau \to K^+ \bar{K^0} \nu\) using only two inputs as the \(\rho\) and \(K^*\) masses, or the two corresponding rms radii, agree with the experimental data. Using the same number of parameters, the corresponding one loop CPTH calculation cannot explain the $\tau$ data.

Light Hadron Spectroscopy at BESIII

With data of 1.3 billion J/ψ events and 106 million ψ(2S) events collected with the BESIII detector operating at the BEPCII, many different analyses were performed. New baryon states were observed in partial wave analyses of charmonium decays. A comparison between the branching fraction of B(J/ψ → γfo(1710)) to the recent lattice QCD prediction of J/ψ decaying to glueball ground state B(J/ψ → γG(0++)) benefits from new results of J/ψ → γηη. The observation of η' → π+π-π+(π0)π- (π0) via the radiative decay of J/ψ → γη' agrees with the combined model of chiral perturbation theory and vector-meson dominance approach.

Study of the η′→Ve+e− decay with hidden local symmetry model**Supported by National Natural Science Foundation of China (11147008, 11275057, U1332103, U1232101) and Program for Science and Technology Innovation Talents in Universities of Henan Province (2012HASTIT030)

Within the hidden local symmetry framework, the Dalitz decay η′→Ve+e− is studied with the vector meson dominance model. It is found that the partial width Γ(η′→ωe+e−) ≈ 40 eV and branching ratio β(η′→ωe+e−) ≈ 2×10−4, and Γ(η′→ρe+e−) ≈ 10Γ(η′→ωe+e−) and β(η′→ρe+e−) ≈ 10β(η′→ωe+e−). The maximum position of the dilepton distribution is me+e− ≈1.33 MeV. These decays are measurable with the advent of high statistic η′ experiments.

Composite Goldstone dark matter: experimental predictions from the lattice

We study, via first principles lattice simulations, the nonperturbative dynamics of $SU(2)$ gauge theory with two fundamental Dirac flavors. The model can be used simultaneously as a template for composite Goldstone boson dark matter and for breaking the electroweak symmetry dynamically. We compute the form factor, allowing us to estimate the associated electromagnetic charge radius. Interestingly we observe that the form factor obeys vector meson dominance even for the two color theory. We finally compare the model predictions with dark matter direct detection experiments. We find that the composite Goldstone boson dark matter cross sections is constrained by the most stringent direct-detection experiments. Our results are a foundation for quantitative new composite dynamics relevant for model building, and are of interest to current experiments.

Discovery potential of hidden charm baryon resonances via photoproduction

In this work, we study the possibility to find and resonances with hidden charm with mass above 4 GeV in the photon-induced production. The cross sections for the photoproductions of hidden charmed baryons are predicted in the effective Lagrangian approach with the vector meson dominance mechanism. can be produced directly by photon excitation with total cross section about 1 nb. provides an obvious peak near the threshold for photoproduction, which is expected to be checked by the future high precision experiment at JLab 12 GeV. The results will be helpful in the experimental search for the hidden-charmed baryon resonances in the forthcoming experiments at JLab 12 GeV, such as SoLID, and the proposed electron–ion colliders at FAIR and HIAF.

Axial anomaly and vector meson dominance model

A connection between the axial anomaly and the vector meson dominance model is revealed for the processes of pseudoscalar meson-photon transitions. The analytic continuation of the anomaly sum rules, which are exact QCD relations following follow from the dispersive representation of the axial anomaly, to the time-like region is performed. Using these sum rules, the transition form factors of π0, η, and η′ mesons in this region are calculated. A good agreement with the available experimental data is found.

Direct [formula omitted] production in [formula omitted] collisions

Direct production of the charmonium-like state X(3872) in e+e− collisions is considered in the framework of the vector meson dominance model. An order-of-magnitude estimate for the width Γ(X→e+e−) is found to be ≳0.03 eV. The same approach applied to the χc1 charmonium decay predicts the corresponding width of the order 0.1 eV in agreement with earlier estimates. Experimental perspectives for the direct production of the 1++ charmonia in e+e− collisions are briefly discussed.