We apply a modified vector meson dominance (VMD) model to analyze the electromagnetic form factors of the $Λ_c$ hyperon in the time-like reaction $e^+e^-\rightarrow Λ_c^+ \barΛ_c^-$. In the model, we include the contributions from the vector charmed mesons and their excitations $ψ(1S)$, $ψ(2S)$, $ψ(3770)$, $ψ(4040)$, $ψ(4160)$ and $ψ(4415)$. We perform a combined fit to the available data on the Born cross section in reaction $e^+e^-\rightarrow Λ_c^+ \barΛ_c^-$ and the ratio of the electromagnetic form factors $|G_E/G_M|$ to obtain the values of the model parameters. Our results show that the VMD model can simultaneously describe the data of electromagnetic form factors from the Belle and BESIII Collaborations, and the behavior of $|G_E/G_M|$ for the BESIII data can be qualitatively reproduced by the VMD model prediction at the threshold region. Moreover, we predict the single and double polarization observables in $e^+e^-\rightarrow Λ_c^+ \barΛ_c^-$ reactions, which are experimentally accessible in the polarized process. We also obtain the form factors of the $Λ_c$ hyperon in the space-like region via analytic continuing the time-like form factors.
We perform an analysis on the electromagnetic form factors of the $Λ$ hyperon in the time-like reaction $e^+e^-\rightarrow Λ\barΛ$ by using a modified vector meson dominance model. We consider both the intrinsic structure components and the meson clouds components. For the latter one, we not only include the contributions from the $ϕ$ and $ω$ mesons, but also take into account the contributions from the resonance states $ω(1420)$, $ω(1650)$, $ϕ(1680)$ and $ϕ(2170)$. We extract the model parameters by combined fit to the time-like effective form factor $|G_{\rm{eff}}|$, the electromagnetic form…
We study the question whether the phenomenologically successful VMD approach to weak radiative hyperon decays can be made consistent with Hara's theorem and still yield the pattern of asymmetries exhibited by experimental data. It appears that an essential ingredient which governs the pattern of asymmetries is the off-shell behaviour of the input electromagnetic 1/2^- 1/2^+ γcouplings. Although this behaviour can be chosen in such a way that the experimentally observed pattern is obtained, and yet Hara's theorem satisfied, at the same time the approach yields a definite prediction for the size…
Decays of heavy mesons and of heavy hyperons are used to provide tests of the standard model and information about new mixing schemes for the $η$ and $η^{'}$ mesons. These include the two body decays $B_s \to J / ψM$ and $B_d \to J / ψM$, $B \to η(η^{'})K(K^\ast)$ and $Λ_b \to Λη(η^{'})$, semileptonic $D$ decays, and properties of radially excited mesons.
Aspects of Scalar Meson Dominance in semi- and non-leptonic weak pseudoscalar meson decays are shortly discussed on the basis of the Quark-Level Linear Sigma Model.
Vector-Meson-Dominance model contribution to $π^0 \to 4γ$ is calculated. The result confirms old estimates that this contribution is much smaller than the purely electromagnetic photon spliting graph contribution calculated earlier.
Heavy Meson Radiative Decays and Light Vector Meson Dominance
在含有轻矢量粒子的重介子有效手征拉格朗日量中引入了电磁相互作用。一个合适的矢量介子优势的概念制定。利用实验$D^* \ra D \, γ$分支比得到了对重介子-轻矢量和重介子-轻赝标耦合常数的约束。这些限制进行了比较，从半轻子跃迁振幅估计值，以及从光介子耦合模式的扩展。并将其应用于"束缚态“模型中的重子谱。
A review of recent precision measurements of the electromagnetic form factors of the mesons, pion and kaon, and the hyperons, $Λ^0$, $Σ^0$, $Σ^+$, $Ξ^-$, $Ξ^0$, $Ω^-$, at large timelike momentum transfers is presented. Evidence is found for diquark correlations in $Λ^0$, $Σ^0$ hyperons.
The decay $η'\rightarrowπ^0γγ$ is studied theoretically in the framework of the Vector Meson Dominance model (VMD). We find theoretically a significant contribution of the interference of $ω-ρ$ and provide theoretical Dalitz-plots. Comparison with the experimental results of BES-III \cite{BES-III} is done. We find some tension between our predicted value and the observed result. Our calculations can be also checked using the data of GAMS-$4π$.
A current-current correlator with the quantum numbers of the omega meson is studied in a nuclear medium. Using weighted finite energy sum rules and dispersion relations for the current-nucleon forward scattering amplitude it is shown that strict vector meson dominance and QCD sum rules are incompatible with each other. This implies that at least one of these concepts -- which are both very powerful in the vacuum -- has to fade in the nuclear environment.
The hypothesis is scrutinized that the weak interaction of hadronic systems at low energies is dominated by the coupling of the pseudoscalar, vector, and axial-vector mesons to the weak gauge bosons. The strength of the weak coupling of the rho(770) meson is uniquely determined by vector-meson dominance in electromagnetic interactions; flavor and chiral symmetry breaking effects modify the coupling of other vector mesons and axial-vector mesons. Many decay rates are calculated and compared to experimental data and partly to predictions of other models. A parameter-free description of the decay…
After describing the SU(2) linear sigma model (L$σ$M), we dynamically generate it using the B.W. Lee null tadpole sum (characterizing the true vacuum) together with the dimensional regularization lemma. Next we generate the chiral-limiting (CL) nonstrange and strange constituent quark masses ${\hat m}=325.7$ MeV; $m_s=486$ MeV away from the CL. Finally, we study vector meson dominance (VMD) and the pion, kaon charge radii and the loop-order $ρ\toπγ$, $π^0\toγγ$ amplitudes in the quark model. Lastly, we verify this procedure using tree-order VMD graphs.
Using the calculated values of the strong coupling constants of the heavy sextet spin-3/2 baryons to sextet and antitriplet heavy spin-1/2 baryons with light mesons within the light cone QCD sum rules method, and vector meson dominance assumption, the radiative decay widths are calculated. These widths are compared with the "direct" radiative decay widths predicted in the framework of the light cone QCD sum rules.
The near-threshold $e^+e^- \to Λ\barΛ$ reaction is studied with the assumption that the production mechanism is due to a near-$Λ\barΛ$-threshold bound state. The cross section of $e^+e^- \to Λ\barΛ$ reaction is parametrized in terms of the electromagnetic form factors of $Λ$ hyperon, which are obtained with the vector meson dominance model. It is shown that the contribution to the $e^+e^- \to Λ\barΛ$ reaction from a new narrow state with quantum numbers $J^{PC}=1^{--}$ is dominant for energies very close to threshold. The mass of this new state is around 2231 MeV, which is very close to the ma…
Extended vector meson dominance model, that allows to describe the electromagnetic form factors of nucleons obeying the asymptotic quark counting rule prescriptions and contains the minimal number of free parameters, is presented. We get a reasonable fit of form factors over experimentally available space-like region of momentum transfer and get also reasonable results in the time-like region.
We prove that recent data demonstrates unequivocally that the scalar meson $f_0$(980) is mostly composed of $s\bar{s}$ quarks and that the coupling of $f_0$ to photons and mesons is in agreement with the linear sigma model.
We discuss and test the assumptions of the chirally normalized vector meson dominance model (CN-VMD), as it is used for tau decays. We compare the CN-VMD amplitudes with those using on-shell couplings, derived directly from experimental data. We discuss in detail the $3π$, $K K π$ and $2π$ final states. We suggest that the true values for the $K_1$ widths might be larger than those quoted in the Review of Particle Physics.
We study a vector dominance model which predicts a fairly large number of currently interesting decay amplitudes of the types S -> γγ, V -> S γand S -> V γ, where S and V denote scalar and vector mesons, in terms of three parameters. As an application, the model makes it easy to study in detail a recent proposal to boost the ratio Gamma(phi -> f_0 gamma) / Gamma(phi -> a_0 gamma) by including the isospin violating a_0 - f_0 mixing. However we find that this effect is actually small in our model.
Non-exotic scalar-meson resonances in S-wave meson-meson scattering are studied in the light of a unitarised Schroedinger model. The resulting poles in the scattering matrices, by analytical continuation into the complex-energy plane, are grouped into nonets of isoscalar, isodoublet, and isotriplet resonances. All singularities can be related to quark-antiquark confinement states, the light-quark nonet of which has ground states at 1.3 to 1.4 GeV and level spacings of some 300-400 MeV, except for a nonet of light scalar mesons below 1 GeV. All non-exotic S-wave resonances reported by experimen…
In this paper, we address the universality problem in the mass-mixing representation of vector meson dominance. First we stress the importance of using physical (mass eigenstate) fields in order to get the correct $q^2$ dependence of the pion form factor. Then we show that, when a direct coupling of the (proto-)photon to the pions is included, it is not necessary to invoke universality. Our method is similar to the delocalization idea in some deconstrunction theories.
Motivated by recent estimates of the isospin-violating process tau \to eta pi nu_tau, mostly relying on the rho and a_0 dominance of the relevant form factors near threshold, we present an assessment for the branching ratio that accounts for additional, potential, effects from the lowest radial excitations rho(1450) and a_0(1450), respectively, also lying in the decay phase space.
We investigate the reaction of $γN \to K \bar{K} N$ focusing on the photoproduction of $Λ(1520)$ and putative exotic $Θ(1540)$. We consider various background production mechanisms including the production of vector mesons, tensor mesons, and other $Λ$ and $Σ$ hyperons. We discuss the angular distribution of $Λ(1520)$ photoproduction cross section and the radiative decays of $Λ(1520)$. We also discuss what we expect for the invariant mass distributions if the $Θ(1540)$ is formed in the reaction, with the parameters studied so far. We find that the peak in the $KN$ invariant mass distribution, …
A model is developed for electromagnetic form factors of the charged and neutral K-mesons. The formalism is based on ChPT Lagrangians with vector mesons. The form factors, calculated without fitting parameters, are in a good agreement with experiment for space-like and time-like photon momenta. Contribution of the two-kaon channels to the muon anomalous magnetic moment a_μis calculated.
We summarize some features of the vector meson dominance model which was recently proposed for studying radiative decays involving the scalar mesons. Using the experimental values of $Γ(a_0 \to γγ)$, $Γ(f_0 \to γγ)$ and $Γ(ϕ\to a_0 γ)$ as inputs, we show that the model predicts a large hierarchy between $Γ(a_0 \to ωγ)$ and $Γ(a_0 \to ργ)$ as well as between $Γ(f_0 \to ωγ)$ and $Γ(f_0 \to ργ)$.
Historically vector-meson physics arose along two different paths to be reviewed in Sections 1 and 2. In Section 3, the phenomenological consequences will be discussed with an emphasis on those aspects of the subject matter relevant in present-day discussions on deep inelastic scattering in the diffraction region of low values of the Bjorken variable.
The vacuum fluctuation (VF) effects on the properties of the hyperonic neutron star matter are investigated in the framework of the relativistic mean field (RMF) theory. The VF corrections result in the density dependence of in-medium baryon and meson masses. We compare our results obtained by adopting three kinds of meson-hyperon couplings. The introduction of both hyperons and VF corrections soften the equation of state (EoS) for the hyperonic neutron star matter and hence reduce hyperonic neutron star masses. The presence of the $δ$ field enlarges the masses and radii of hyperonic neutron s…
A thermal Finite Energy QCD Sum Rule is used to determine the temperature behaviour of the $ωρπ$ strong coupling. This coupling decreases with increasing $T$ and vanishes at the critical temperature, a likely signal for quark deconfinement. This is then used in the Vector Meson Dominance (VMD) expression for the $π^0 \to γγ$ amplitude, which is also found to vanish at the critical temperature, as expected. This result supports the validity of VMD at $T \neq 0$. However, if VMD would not hold at finite temperature, then there is no prediction for the $π^0 \to γγ$ amplitude.
The measured electromagnetic form factors of $Λ$ hyperon in the time-like region are significantly deviated from pQCD prediction. We attribute the non-vanishing cross section near threshold to be the contribution of below-threshold $ϕ$(2170) state, supporting its exotic structure. Above the threshold, we find significant role of a wide vector meson with the mass of around 2.34 GeV, which would be the same state present in $p\bar{p}$ annihilation reactions. As a result, we give a satisfactory description of the behavior of existing data without modifying pQCD expectation.
Based on the recently measurements of the $e^{+} e^{-} \to Σ^{+} \barΣ^{-}$ and $e^{+} e^{-} \to Σ^{-} \barΣ^{+}$ processes, the electromagnetic form factors of the hyperon $Σ^+$ and $Σ^-$ in the timelike region are investigate by using the vector meson dominance model. We have included the contributions from the $ρ$, $ω$ and $ϕ$ mesons. The model parameters are determined with the BESIII experimental data on the timelike effective form factors $|G_{\rm eff}|$ of $Σ^{+}$ and $Σ^{-}$ for center-of-mass energy from 2.3864 to 3.02 GeV. Then, we analytically continue the electromagnetic form facto…
In this work we extend our formalism to study meson-baryon interactions by including $s$- and $u$-channel diagrams for pseudoscalar-baryon systems. We study the coupled systems with strangeness $-1$ and focus on studying the isospin-1 resonance(s), especially in the energy region around 1400 MeV. By constraining the model parameters to fit the cross section data available on several processes involving relevant channels, we find resonances in the isoscalar as well as the isovector sector in the energy region around 1400 MeV.
We use the meson cloud model and the Sullivan mechanism to estimate the sea flavor asymmetry in the Σ^+ baryon and calculate the distribution functions of both sea and valence quarks. We find large deviations from SU(3).
Encouraged by a recent observation of the B_c^+ -> B_s^0 + pi^+ decay by the LHCb collaboration we present the meson dominance predictions for other weak decays of the B_c^+ into B_s^0 or B^0 in the form of branching ratios to the observed decay.
We revisit the electroweak precision tests for Higgsless models of strong EWSB. We use the Vector Meson Dominance approach and express S and T via couplings characterizing vector and axial spin-1 resonances of the strong sector. These couplings are constrained by the elastic unitarity and by requiring a good UV behavior of various formfactors. We pay particular attention to the one-loop contribution of resonances to T (beyond the chiral log), and to how it can improve the fit. We also make contact with the recent studies of Conformal Technicolor. We explain why the second Weinberg sum rule nev…
Motivated by the experimental measurements of $D^0$ radiative decay modes we have proposed a model to study the $D^0\to \bar{K}^{*0}γ$ decay, by establishing a link with $D^0\to \bar{K}^{*0}V$ $(V=ρ^0,\, ω)$ decays through the vector meson dominance hypothesis. In order to do this properly, we have used the Lagrangians from the local hidden gauge symmetry approach to account for $Vγ$ conversion. As a result, we have found the branching ratio $\mathcal{B}[D^0\to \bar{K}^{*0}γ] =(1.55 - 3.44)\times 10^{-4}$, which is in fair agreement with the experimental values reported by Belle and Babar coll…
A renormalizable non-abelian vector meson dominance model coupled to pions is constructed which exhibits a ${\rm SO}\left(4,3\right)$ vacuum symmetry. Tree-level predictions for $p$-$p$ scattering lengths and slopes at leading order are in reasonable agreement with experiment.
It is explicitly shown that either the approximate solution of the integral equation for the inverse of the pion form factor, or the result of the Padé 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 $ππ$ scattering. …
By using a thermal Finite Energy QCD Sum Rule, we are able to establish the temperature dependence of the $g_{ωρπ}(T)$ strong coupling. It turns out that this coupling decreases as a function of temperature, vanishing at the critical temperature. This corresponds to a possible deconfining phenomenological signal. This result, together with the Vector Meson Dominance (VMD) expression for the amplitude $π^{0} \to γγ$, allows us to establish that this amplitude also vanishes at the critical temperature, in agreement with previous independent analysis. This results supports, once again, the validi…
A Finite Energy QCD sum rule at non-zero temperature is used to determine the $q^2$- and the T-dependence of the $ρππ$ vertex function in the space-like region. A comparison with an independent QCD determination of the electromagnetic pion form factor $F_π$ at $T \neq 0$ indicates that Vector Meson Dominance holds to a very good approximation at finite temperature. At the same time, analytical evidence for deconfinement is obtained from the result that $g_{ρππ}(q^{2},T)$ vanishes at the critical temperature $T_c$, independently of $q^{2}$. Also, by extrapolating the $ρππ$ form factor to $q^2 =…
By using a parametrization of the non-linear Walecka model which takes into account the binding energy of different hyperons, we present a study of particle production yields measured in central Au-Au collision at RHIC. Two sets of different hyperon-meson coupling constants are employed in obtaining the hadron production and chemical freeze-out parameters. These quantities show a weak dependence on the used hyperon-meson couplings. Results are in good overall accordance with experimental data. We have found that the repulsion among the baryons is quite small and, through a preliminary analysis…
The use of Pade Approximants for the analysis of the pion vector form-factor is discussed and justified in this talk. The method is tested first in a theoretical model and applied then on real experimental data. It is shown how the Pade Approximants provide a convenient and reliable framework to incorporate both low and high energy information in the euclidean region, leading to improved determinations of the low energy parameters such as, e.g., the quadratic radius <r^2>^pi_V.
Recent results by Benayoun et al. comparing the predictions of a range of existing models based on the Vector Meson Dominance hypothesis are summarized and discussed. These are compared with data on e+ e- -> pi+ pi- and e+ e- -> mu+ mu- cross-sections and the phase and near-threshold behavior of the timelike pion form factor, with the aim of determining which (if any) of these models is capable of providing an accurate representation of the full range of experimental data. We find that, of the models considered, only that proposed by Bando et al. is able to consistently account for all informa…
We calculate magnetic moments of nucleons and hyperons and N -> Delta + gamma transition characteristics using a manifestly Lorentz covariant chiral quark approach for the study of baryons as bound states of constituent quarks dressed by a cloud of pseudoscalar mesons.
We summarize our recent results for the quark loop part of the light-by-light scattering contribution as well as the hadronic vacuum polarisation contributions to the anomalous magnetic moment of the muon. In particular we focus on the role played by the momentum dependence of the quark- and quark-photon vertex dressing functions. We give a detailed comparison of the Dyson-Schwinger description of this contribution to the corresponding picture emerging from hadronic models in particular the extended Nambu--Jona-Lasonio model (ENJL). We find that the details of the momentum dependence are impor…
The concept of incomplete vector-meson dominance and Regge models is applied to the transition form factor of the pion. First, we argue that variants of the chiral quark model fulfilling the chiral anomaly may violate the Terazawa-West unitarity bounds, as these bounds are based on unverified assumptions for the real parts of the amplitudes, precluding a possible presence of polynomial terms. A direct consequence is that the transition form factor need not necessarily vanish at large values of the photon virtuality. Moreover, in the range of the BaBar experiment, the Terazawa-West bound is an …
The dispersive representation of axial anomaly leads to the anomaly sum rules (ASRs), exact nonperturbative relations in QCD. The analytical continuation of the ASRs to the time-like region is performed. The transition form factors of $π^0$, $η$ and $η'$ mesons in this region are calculated. A good agreement with the available experimental data is found. Based on the ASRs, we have provided the foundations for the vector meson dominance model in these processes.
We argue that a Regge-pole modification of the VDM puts on equal footing the asymptotic behaviour of electromagnetic and neutral vector meson currents.
We give a joint description of weak radiative (WR) and nonleptonic (NL) hyperon decays (HD) in broken SU(3). The two groups of decays are linked via $SU(2)_W$ spin symmetry and vector meson dominance (VMD). We use experimental information on the parity-conserving (p.c.) NLHD amplitudes to fix the corresponding WRHD amplitudes. With the latter known, the data on the WRHD branching ratios and asymmetries permit us to determine the parity-violating (p.v.) WRHD amplitudes in terms of two parameters corresponding to the two-quark and single-quark transitions. We obtain a good description of the dat…
A systematic study of global spin polarizations and correlations of hadrons with different spins in relativistic heavy ion collisions
Institute of Frontier and Interdisciplinary Science, Key Laboratory of Particle Physics and Particle Irradiation (MOE), Shandong University（山东大学前沿交叉科学研究中心，粒子物理与粒子辐照教育部重点实验室）
In this paper we address the question: ``do the limits on technirho production at the Tevatron mean what we think they do ?'' These limits are based on calculations that rely on Vector Meson Dominance (VMD). VMD was invented in order to describe the interaction of electrons with hadrons (the rho meson and pions). The method has been used also as a tool in the study of Technicolor phenomenology. Nevertheless there are evidences in the sense that, even in its original, context VMD is not completely realized. In this work we investigate the consequences of a deviation from complete VMD for the ph…
We consider chiral perturbation theory with an explicit broad $σ$-meson and study its contribution to the scalar form factors of the pion and the nucleon. Our goal is to learn more about resonance saturation in the scalar sector.
The total photoabsorption cross section on the nucleon is studied using nondiagonal GVDM. Vector meson-nucleon scattering amplitudes are calculated in two-gluon exchange approximation of QCD. The off-diagonal transitions of diffraction dissociation type between different vector mesons and their contributions to the expression for the total photoabsorption cross section on the nucleon are also calculated. It is shown that destructive interference of diagonal and off-diagonal terms is not effective. The main conclusion is that a p-cut-off in gamma-quark antiquark transition is necessary for obta…
