Vector Meson Dominance Research Articles

Bc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{B_c}$$\\end{document} to A transition form factors and semileptonic decays in self-consistent covariant light-front approach

We present a comprehensive analysis of the semileptonic weak decays of Bc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c$$\\end{document} meson decaying to axial-vector (A) mesons for bottom-conserving and bottom-changing decay modes. We employ self-consistent covariant light-front quark model (CLF QM) that uses type-II correspondence to eliminate inconsistencies in the traditional type-I CLF QM. As a fresh attempt, we test the self-consistency in CLF QM through type-II correspondence for Bc→A\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow A$$\\end{document} meson transition form factors. We establish that in type-II correspondence the form factors for longitudinal and transverse polarization states are numerically equal and are free from zero-mode contributions, which confirms the self-consistency of type-II correspondence for Bc→A\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow A$$\\end{document} transition form factors. Furthermore, we ascertain that the problems of inconsistency and violation of covariance of CLF QM within the type-I correspondence are resolved in type-II correspondence for Bc→A\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow A$$\\end{document} transitions. We thoroughly investigate the effects of self-consistency between type-I and type-II schemes using a comparative analysis. In this investigation, we employ a direct calculation approach to determine the form factors within the space-like region. Subsequently, we employ a vector meson dominance (VMD)-inspired three-parameter form to extrapolate these form factors into the physically accessible region. This enables us to study the q2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q^2$$\\end{document} dependence of the form factors in weak hadronic currents for the whole accessible kinematic range for both bottom-conserving as well as bottom-changing transitions. In addition, we extend our analysis to predict the branching ratios of the semileptonic weak decays of Bc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c$$\\end{document} meson involving axial-vector meson in the final state to quantify the effects of self-consistency in these decays that were not studied before. We evaluate the lepton mass effect on these branching ratios and various other important physical observables, such as forward-backward asymmetries, lepton-side convexity parameter, asymmetry parameter, and longitudinal polarization asymmetries and fractions. Finally, we obtain the lepton flavor universality ratios for various decays.

ρ meson magnetic dipole moment from BaBar e+e−→π+π−π0π0 cross section measurement

We obtain the value of the magnetic dipole moment of the ρ meson, using data from the collaboration for the e+e−→π+π−2π0 process. The considered center of mass energy range is from 0.9 to 1.8 GeV. We describe the γ*→4π vertex using a vector meson dominance model, including the intermediate resonant contributions relevant at these energies. We find μρ=2.7±0.3 in e/2mρ units. We improve on the previous extracted value, where preliminary data from the same collaboration was used, by considering definite data, better grounded values of the parameters involved, and an explicit gauge invariant description of the process. Published by the American Physical Society 2024

Photoproduction of the X(3872) beyond vector meson dominance: the open-charm coupled-channel mechanism

Hidden-charm exotic hadrons will be searched for and investigated at future electron–ion colliders. For instance, the X(3872) can be produced through the exclusive process γ p → X(3872)p. The vector meson dominance model has been commonly employed in estimating the cross sections of such processes. However, the coupled-channel production mechanism through open-charm meson-baryon intermediate states may play a crucial role. To assess the significance of such contributions, we estimate the cross section of the γ p → X(3872)p reaction assuming the coupled-channel mechanism. For energies near the threshold, the total cross section is predicted to be of tens of nanobarns for γ p → X(3872)p, which can be measured at future experimental facilities. Furthermore, the open-charm coupled-channel mechanism leads to a distinct line shape of the total cross section that can be utilized to reveal the production dynamics.

Systematic investigation of trace anomaly contribution in nucleon mass

In this work, under the framework of the vector meson dominance model, the trace anomaly contribution value inside neutrons is extracted for the first time based on vector meson photoproduction data. Furthermore, we systematically compare and analyze the trace anomaly contributions of protons and neutrons. The results show that the trace anomaly contributions of protons and neutrons are close, which indirectly confirms that their internal structures and dynamic properties may have certain similarities. In addition, the main factors affecting the extraction of the trace anomaly contribution of nucleons are discussed in detail. This study not only provides a theoretical basis for us to better understand the source of nucleon mass but also makes a useful exploration and discussion on how to extract the trace anomaly contribution of nucleons more accurately in the future. Published by the American Physical Society 2024

XYZ spectroscopy at electron-hadron facilities. III. Semi-inclusive processes with vector exchange

Inclusive production processes will be important for the first observations of XYZ states at new generation electron-hadron colliders, as they generally benefit from larger cross sections than their exclusive counterparts. We make predictions of semi-inclusive photoproduction of the χc1(1P) and X(3872), whose peripheral production is assumed to be dominated by vector exchanges. We validate the applicability of vector meson dominance in the axial-vector charmonium sector and calculate production rates at center-of-mass energies relevant for future experimental facilities. We find the semi-inclusive cross sections near the threshold to be enhanced by a factor of ∼2–3 compared to the exclusive reaction and well-suited for a first observation in photoproduction. Published by the American Physical Society 2024

Baryonic dark forces in electron-beam fixed-target experiments

New GeV-scale dark forces coupling predominantly to quarks offer novel signatures that can be produced directly and searched for at high-luminosity colliders. We compute the photon-proton and electron-proton cross sections for producing a GeV-scale gauge boson arising from a U(1)B gauge symmetry. Our calculation relies on vector meson dominance and a phenomenological model for diffractive scattering used for vector-meson photoproduction. The parameters of our phenomenological model are fixed by performing a Markov Chain Monte Carlo fit to existing exclusive photoproduction data for ω and ϕ mesons. Our approach can be generalized to other GeV-scale dark gauge forces.

E+e−→Λc+Λ¯c− Cross Sections and the Λc+ Electromagnetic Form Factors within the Extended Vector Meson Dominance Model

Within the extended vector meson dominance model, we investigate the e+e−→Λc+Λ¯c− reaction and the electromagnetic form factors of the charmed baryon Λc+ . The model parameters are determined by fitting them to the cross sections of the process e+e−→Λc+Λ¯c− and the magnetic form factor |G M| of Λc+ . By considering four charmonium-like states, called ψ(4500), ψ(4660), ψ(4790), and ψ(4900), we can well describe the current data on the e+e−→Λc+Λ¯c− reaction from the reaction threshold up to 4.96 GeV. In addition to the total cross sections and |G M|, the ratio |G E/G M| and the effective form factor |G eff| for Λc+ are also calculated, and found that these calculations are consistent with the experimental data. Within the fitted model parameters, we have also estimated the charge radius of the charmed Λc+ baryon.

Dilepton production in proton-proton reaction at 4.5 GeV with the HADES spectrometer

Spectra of dileptons emitted in hadron collisions are important tool to study electromagnetic decays of resonances and the validity of the Vector Meson Dominance model. Furthermore, they provide reference spectra for the hot and dense (heavy-ion A+A collisions) and cold nuclear matter (p+A collisions). In February 2022, proton-proton reactions at 4.5 GeV beam kinetic energy were measured by HADES experiment. The aim of the analysis is to study the specific channels that produced dileptons, such as baryonic resonance Dalitz decays (Δ/N* → Ne+e−) and vector meson decays (ρ/ω/φ→ e+e−). In addition, the investigations of dielectron production above the φ meson mass will be enabled. In this contribution, different steps of the e+e− pair reconstruc tion are discussed.

Coordinate-space calculation of QED corrections to the hadronic vacuum polarization contribution to (g − 2)μ with SU(3) flavor symmetry

Lattice QCD (LQCD) has proven to be an important tool in understanding the tension between the experimental value for the anomalous magnetic moment of the muon (g − 2)μ and its prediction from the standard model. The lattice provides a non-perturbative method for evaluating the hadronic contributions to (g − 2)μ, which contributes the largest amount to the uncertainty of the theoretical prediction. Among these the hadronic vacuum polarization aμHVP is the dominant contribution. In order to match the uncertainty of the experiment, lattice QCD needs to reach sub-percent precision. This requires the calculation of QED corrections to aμHVP, which are represented by additional Feynman diagrams. We present a lattice calculation of the UV-finite (2+2) diagram at the SU(3) flavor symmetric point and compare this to the pseudoscalar meson exchange model with a vector-meson dominance parametrization of the transition form factor.

Proving Rho Meson Is a Dynamical Gauge Boson of Hidden Local Symmetry

The rho meson has long been successfully identified with a dynamical gauge boson of Hidden Local Symmetry (HLS) Hlocal in the non-linear sigma model G/H gauge equivalent to the model having the symmetry Gglobal×Hlocal, with G=[SU(2)L×SU(2)R]≃O(4),H=SU(2)V≃O(3). However, under a hitherto unproven assumption that its kinetic term is dynamically generated, together with an ad hoc choice of the auxiliary field parameter “a=2”, we prove this assumption, thereby solving the long-standing mystery. The rho meson kinetic term is generated simply by the large N limit of the Grassmannian model G/H=O(N)/[O(N−3)×O(3)] gauge equivalent to O(N)global×[O(N−3)×O(3)]local, extrapolated to N=4, O(4)global×O(3)local, with all the phenomenologically successful “a=2 results”, i.e., ρ-universality, KSRF relation, and the Vector Meson Dominance, realized independently of the parameter “a”. This in turn establishes validity of the large N dynamics at the quantitative level directly by the experiments. The relevant cutoff reads Λ≃4πFπ for N=4, which is regarded as a matching scale of the HLS as a “magnetic dual” to QCD. Skyrmion is stabilized by such a dynamically generated rho meson without recourse to the underlying QCD, a further signal of the duality. The unbroken phase with a massless rho meson may be realized as a novel chiral-restored hadronic phase in the hot/dense QCD.

From Ds → γ in lattice QCD to Bs → μμγ at high q2

We use a recent lattice determination of the vector and axial Ds → γ form factors at high squared momentum transfer q2 to infer their Bs → γ counterparts. To this end, we introduce a phenomenological approach summarized as follows. First, we describe the lattice data with different fit templates motivated by vector-meson dominance, that is expected to hold in the high-q2 region considered. We identify reference fit ansaetze with one or two physical poles, that we validate against alternative templates. Then, the pole residues can be unambiguously related to the appropriate couplings involving the pseudoscalar, the vector mesons concerned, and the photon — or tri-couplings — and the latter can be expressed as sums over quark magnetic moments, weighed by their e.m. charges. This description obeys a well-defined heavy-quark scaling, that allows to parametrically scale up the form factors to the Bs → γ case. We discuss a number of cross-checks of the whole approach, whose validation rests ultimately in a first-principle determination, e.g. in lattice QCD. Finally, we use our obtained form factors to reassess the SM prediction of ℬ(Bs → μ+μ−γ) in the range sqrt{q^2}in [4.2, 5.0] GeV, where an experimental measurement is awaited.

Cornering large-Nc QCD with positivity bounds

The simple analytic structure of meson scattering amplitudes in the large-Nc limit, combined with positivity of the spectral density, provides precise predictions on low-energy observables. Building upon previous studies, we explore the allowed regions of chiral Lagrangian parameters and meson couplings to pions. We reveal a structure of kinks at all orders in the chiral expansion and develop analytical tools to show that kinks always correspond to amplitudes with a single light pole. We build (scalar- and vector-less) deformations of the Lovelace-Shapiro and Coon UV-complete amplitudes, and show that they lie close to the boundaries. Moreover, constraints from crossing-symmetry imply that meson couplings to pions become smaller as their spin increases, providing an explanation for the success of Vector Meson Dominance and holographic QCD. We study how these conclusions depend on assumptions about the high-energy behavior of amplitudes. Finally, we emphasize the complementarity between our results and Lattice computations in the exploration of large-Nc QCD.

Vector meson-nucleon scattering length $$|\alpha _{VN}|$$ and trace anomalous energy contribution to the nucleon mass $$T_{A}$$

Low-energy scattering processes of vector meson and nucleon are an important window for studying non-perturbative QCD. The interaction of vector meson with nucleon, vector meson-nucleon scattering length $|\alpha_{VN}|$, is an important component of the study of hadronic interactions. Nowadays many scattering length values $|\alpha_{VN}|$ have been reported using the recent photoproduction experiment data or quasi data. In addition, the study of trace anomalous energy contribution to the proton mass is also a hot topic in non-perturbative QCD and hadron physics. However, it is difficult to measure proton trace anomalous energy experimentally, and the study of the trace anomaly of proton is still inconclusive. In this study, we established the relationship between the scattering length of the vector meson-proton $|\alpha_{Vp}|$ and the trace anomaly contribution of the proton mass $T_{A}$. With the scattering length values extracted by using the Vector Meson Dominance model, we obtained the trace anomaly contribution of the proton mass $T_{A}$ = (22.8$\%$ $\pm$ 1.2$\%$), which is of similar order of magnitude as the 23$\%$ given by Lattice QCD calculation. We conjecture that the trace anomaly contribution of nucleon is independent of the type of vector meson probe. We hope that high precision measurements of vector meson-nucleon scattering length could give us a better chance to explore the origin of the nucleon mass.

Production of strangeonium phi (1680) state in electromagnetic probe-driven scatterings and hadron–hadron ultraperipheral collisions

In this work, the gamma prightarrow phi (1680) p reaction is systematically studied based on the two gluon exchange model and the pomeron model. The calculation results show that the total cross section of phi (1680) photoproduction can reach more than 80 nb near the center-of-mass energy W=4 GeV, so it is suggested that JLab and other experiments carry out relevant measurements. Moreover, under the framework of the vector meson dominance assumption, the scattering length of phi (1680) and proton interaction is estimated as 0.07pm 0.01 fm from the cross sections predicted by the theoretical models, which is on the same order of magnitude as the phi (1020)-p scattering length. In addition, the total cross section, number of events and rapidity distribution of phi (1680) production are predicted at Electron-Ion colliders (EICs) and ultra-peripheral collisions (UPCs) by using eSTARlight and STARlight code. The study of phi (1680) and relevant properties is of enlightening significance in better understanding the strangeonium family spectrum, and provides necessary data support for the future experiment of EICs and UPCs.

Role of the ρ(1450) in low-energy observables from an analysis in the meson dominance approach

The $\ensuremath{\rho}(1450)$ vector meson (${\ensuremath{\rho}}^{\ensuremath{'}}$) is becoming increasingly important to properly describe precision observables. We analyze a set of decay modes and cross sections, in the low-energy regime, to determine the role played by this meson. This is done through the extraction of the parameters for its description, in the context of the vector meson dominance model and its effective hadronic interactions, involving the low mass lying hadrons ($\ensuremath{\rho}$, $\ensuremath{\omega}$, and $\ensuremath{\pi}$). In a first step, we determine the parameters of the model from ten decay modes which are insensitive to the ${\ensuremath{\rho}}^{\ensuremath{'}}$. Then, we consider the $\ensuremath{\omega}\ensuremath{\rightarrow}3\ensuremath{\pi}$ decay and exhibit the need to extend the description, by incorporating the ${\ensuremath{\rho}}^{\ensuremath{'}}$ and a contact term as prescribed by the Wess-Zumino-Witten anomaly. In a second step, we incorporate the data from the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}3\ensuremath{\pi}$ cross section (as measured by SND, CMD2, BABAR, and BESIII) and then the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ data (as measured by SND and CDM2) to further restrict the ${\ensuremath{\rho}}^{\ensuremath{'}}$ parameters validity region. As an application of the results, we compute the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}4\ensuremath{\pi}$ cross section for the so-called omega channel, measured by BABAR, and find a good description of the data considering the parameters found. As a byproduct, the coupling between $\ensuremath{\rho}$, $\ensuremath{\omega}$, and $\ensuremath{\pi}$ (${g}_{\ensuremath{\rho}\ensuremath{\omega}\ensuremath{\pi}}=11.314\ifmmode\pm\else\textpm\fi{}0.383\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$) is found to be consistent with all the relevant observables, upon the inclusion of the ${\ensuremath{\rho}}^{\ensuremath{'}}$ and the contact term.

First extraction of the proton mass radius and scattering length $$\vert\alpha_{\rho^{0}p}\vert$$ from ρ0 photoproduction

As it involves the lightest physical states excited from the vacuum by the vector quark current, near-threshold ρ0 photoproduction is considered a possible way to research the proton radius and the absolute value of the scattering lengths of the ρ0-proton interaction. In this study, under the assumption of a scalar form factor of dipole form, the value of the proton mass radius is calculated as (0.85 ± 0.06) fm by fitting the differential cross section of the γp → ρ0p reaction at near-threshold energy. For light vector meson photoproduction, because the exchange of a scalar quark-antiquark pair is not suppressed and should dominate the scalar gluon exchange, the radius we extract from ρ0 photoproduction is likely to represent the quark radius of the proton. This fact may explain why the value obtained in this study is very near the proton charge radius. Moreover, the absolute value of the ρ0-proton scattering length $$\vert\alpha_{\rho^{0}p}\vert=(0.31 \pm 0.06)$$ fm is obtained for the first time within the vector meson dominance model. This result disobeys the rule that the absolute value of the vector meson and proton scattering length $$\vert\alpha_{V_{p}}\vert$$ increases with the meson’s mass, which can be attributed to treating the ρ0 meson as a point in the analysis. These results provide useful theoretical information for an in-depth understanding of proton structure and the proton-vector meson interaction.

Leptophobic dark photon interpretation of the [formula omitted] puzzle

The decays of η and η′ mesons provide unique opportunities for testing the properties of low energy Quantum Chromodynamics and for the search of new physics beyond the Standard Model. However, recent experimental results on the rare decays of η(′)→π0(η)γγ cannot be self-consistently described by the combination of the Vector Meson Dominance and Linear Sigma Model employing the same set of parameters. We show that this tension can be attributed to the presence of a leptophobic dark photon B, and find representative values of the parameters which provide consistent description of these three decays, simultaneously. Unlike existing strategies of Dalitz analysis searching for the bump at mB, we propose the usage of mismatch between these decays to constrain the parameters of the hypothetical dark photon. Additionally, we discuss possible signatures of sub-GeV B boson in heavy meson decays.

Dilepton decay of low-mass ρ mesons

The HADES Collaboration has extracted dilepton mass spectra for ${\ensuremath{\pi}}^{\ensuremath{-}}$ induced reactions on the proton from a comparison of data taken on C and ${\mathrm{CH}}_{2}$ targets. The spectra were interpreted in terms of different versions of vector-meson dominance. Here we present results obtained from the theory and generator gibuu. We first check the subtraction procedure used and then discuss the obtained mass spectra for the proton target. We point out that any conclusions on the version of VMD requires the knowledge of the $\ensuremath{\rho}$ spectral function in the interesting mass region.

Two-photon decay of X(6900) from light-by-light scattering at the LHC

The LHCb Collaboration has recently discovered a structure around 6.9 GeV in the double-$J/\ensuremath{\psi}$ mass distribution, possibly a first fully charmed tetraquark state $X(6900)$. Based on vector-meson dominance (VMD) such a state should have a significant branching ratio for decaying into two photons. We show that the recorded LHC data for the light-by-light scattering may indeed accommodate for such a state, with a $\ensuremath{\gamma}\ensuremath{\gamma}$ branching ratio of order of ${10}^{\ensuremath{-}4}$, which is larger even than the value inferred by the VMD. The spin-parity assignment ${0}^{\ensuremath{-}+}$ is in better agreement with the VMD prediction than ${0}^{++}$, albeit not significantly at the current precision. Further light-by-light scattering data in this region, clarifying the nature of this state, should be obtained in the Run 3 and probably in the high-luminosity phase of the LHC (Run 4 etc.).

Observation of the hindered electromagnetic Dalitz decay ψ(3686)→e+e−ηc

Using a data sample of (448.1±2.9)×106 ψ(3686) decays collected at an e+e− center-of-mass energy of 3.686 GeV by the BESIII detector at Beijing Electron Positron Collider II, we report an observation of the hindered electromagnetic Dalitz decay ψ(3686)→e+e−ηc with a significance of 7.9σ. The branching fraction is determined to be B(ψ(3686)→e+e−ηc)=(3.77±0.40stat±0.18syst)×10−5, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the ψ(3686) and the ηc, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of ηc decays.Received 26 August 2022Accepted 9 November 2022DOI:https://doi.org/10.1103/PhysRevD.106.112002Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBranching fractionElectromagnetic transitionsPhysical SystemsQuarkoniaPropertiesForm factorsTechniquesLepton collidersParticles & Fields