Electromagnetic Form Factors Of Mesons Research Articles

QCD Predictions for Meson Electromagnetic Form Factors at High Momenta: Testing Factorization in Exclusive Processes.

We report the first lattice QCD computation of pion and kaon electromagnetic form factors, F_{M}(Q^{2}), at large momentum transfer up to 10 and 28 GeV^{2}, respectively. Utilizing physical masses and two fine lattices, we achieve good agreement with JLab experimental results at Q^{2}≲4 GeV^{2}. For Q^{2}≳4 GeV^{2}, our results provide abinitio QCD benchmarks for the forthcoming experiments at JLab 12GeV and future electron-ion colliders. We also test the QCD collinear factorization framework utilizing our high-Q^{2} form factors at next-to-next-to-leading order in perturbation theory, which relates the form factors to the leading Fock-state meson distribution amplitudes. Comparisons with independent lattice QCD calculations using the same framework demonstrate, within estimated uncertainties, the universality of these nonperturbative quantities.

Nuclear medium meson structures from the Schwinger proper-time Nambu–Jona-Lasinio model

In this paper, we report the results of our study on the nuclear medium modifications of the meson electromagnetic form factors in the framework of the Nambu–Jona-Lasinio model with the help of the Schwinger proper-time regularization scheme to tame the loop divergence and simulate the effect of QCD confinement. In our current approach, the meson structure and nuclear medium are constructed in the same Nambu–Jona-Lasinio model at the quark level. We examine the free-space and in-medium charge radii of kaon and pion, the spacelike elastic electromagnetic form factors of kaon and pion, and their quark-sector form factors, which reflect their internal structures. By comparing our result to experimental data, we found that the free-space elastic electromagnetic form factors of the mesons are consistent with the data, while the in-medium elastic electromagnetic form factors of the mesons are found to decrease as the nuclear matter density increases, leading to a rise of meson charge radius, which is consistent with the prediction of other theoretical calculations. We also predict the axial nucleon coupling constant gA in nuclear medium computed via the Goldberger-Treiman relation, which is crucial for searching the neutrinoless double beta decay (0νββ). Published by the American Physical Society 2024

The electromagnetic form factors of heavy-light pseudo-scalar and vector mesons

We systematically investigate the electromagnetic form factors of heavy-light pseudo-scalar and vector mesons within the Dyson-Schwinger/Bethe-Salpeter equations framework for the first time. It is found that the charge radius of vector meson is larger than that of its pseudo-scalar counterpart. In heavy-light systems, the flavor symmetry breaking will lead to a splitting of the form factor of different quark, and the distribution range of lighter and heavier quark gradually expands and contracts, respectively. The competition between them together generates the electromagnetic form factors of meson. Our results can be compared with other theoretical calculations and future experimental data.

An Assessment of Pseudoscalar and Vector Meson Electromagnetic Form Factors

An Assessment of Pseudoscalar and Vector Meson Electromagnetic Form Factors

The next-to-leading order corrections to ρ meson electromagnetic form factors in the kT factorization approach

In this paper we calculate the next-to-leading-order (NLO) corrections to ρ-meson electromagnetic form factors by employing the kT factorization approach. We find that the NLO correction to Fi(Q2)(i=LT,TL) is around 30% of the leading-order (LO) contribution in the region Q2>2GeV2. The NLO correction to FLL(Q2) is close to 20% of the LO one in the region Q2>3GeV2. The NLO radiative corrections to the electric, magnetic, and quadruple form factors Fj(Q2)(j=1,2,3) are sizeable in magnitude and agree with those from other approaches.

Chiral behavior of K→πlν decay form factors in lattice QCD with exact chiral symmetry

We calculate the form factors of the K→πlν semileptonic decays in three-flavor lattice QCD and study their chiral behavior as a function of the momentum transfer and the Nambu-Goldstone boson masses. Chiral symmetry is exactly preserved by using the overlap quark action, which enables us to directly compare the lattice data with chiral perturbation theory (ChPT). We generate gauge ensembles at a lattice spacing of 0.11 fm with four pion masses covering 290–540 MeV and a strange quark mass ms close to its physical value. By using the all-to-all quark propagator, we calculate the vector and scalar form factors with high precision. Their dependence on ms and the momentum transfer is studied by using the reweighting technique and the twisted boundary conditions for the quark fields. We compare the results for the semileptonic form factors with ChPT at next-to-next-to-leading order in detail. While many low-energy constants appear at this order, we make use of our data of the light meson electromagnetic form factors in order to control the chiral extrapolation. We determine the normalization of the form factors as f+(0)=0.9636(36)(-35+57) and observe reasonable agreement of their shape with experiment.

The K-meson form factor and charge radius: linking low-energy data to future Jefferson Laboratory measurements

Starting from a successful model of the pi -meson electromagnetic form factor, we calculate a similar form factor, F_{K}(Q^{2}), of the charged K meson for a wide range of the momentum transfer squared, Q^{2}. The only remaining free parameter is to be determined from the measurements of the K-meson charge radius, r_{K}. We fit this single parameter to the published data of the NA-7 experiment which measured F_{K}(Q^{2}) at Q^{2}rightarrow 0 and determine our preferred range of r_{K}, which happens to be close to recent lattice results. Still, the accuracy in the determination of r_{K} is poor. However, future measurements of the K-meson electromagnetic form factor at Q^{2}lesssim 5.5 GeV^{2}, scheduled in Jefferson Laboratory for 2017, will test our approach and will reduce the uncertainty in r_{K} significantly.

Lattice study of D and Ds meson form factors with twisted boundary conditions

We present results on the D and $D_{s}$ meson electromagnetic form factors using $N_{f}=2$ twisted mass Lattice Quantum Chromodynamics (LQCD) gauge configurations. In this simulation, to access spatial components of momenta that are different from the integer multiples of $2\pi /L$ , we apply twisted boundary conditions to compute corresponding correlation functions. Electromagnetic form factors with more small four-momentum transfer are determined, and further we fit the electromagnetic charge radius for D and $D_{s}$ mesons, respectively.

In-Medium $$\varvec{\rho }$$ ρ -Meson Properties in a Light-Front Approach

Properties of \r{ho}-meson in symmetric nuclear matter are investigated within a light-front constituent quark model (LFCQM), using the in-medium input calculated by the quark-meson coupling (QMC) model. The LFCQM used here was previously applied in vacuum to calculate the \r{ho}-meson electromagnetic properties, namely, charge G 0 , magnetic G 1 , and quadrupole G 2 form factors, as well as the electromagnetic radius and decay constant. We predict the in-medium modifications of the \r{ho}-meson electromagnetic form factors in symmetric nuclear matter.

Light meson electromagnetic form factors from three-flavor lattice QCD with exact chiral symmetry

We study the chiral behavior of the electromagnetic (EM) form factors of pions and kaons in three-flavor lattice QCD. In order to make a direct comparison of the lattice data with chiral perturbation theory (ChPT), we employ the overlap quark action that has exact chiral symmetry. Gauge ensembles are generated at a lattice spacing of 0.11 fm with four pion masses ranging between ${M}_{\ensuremath{\pi}}\ensuremath{\simeq}290\text{ }\text{ }\mathrm{MeV}$ and 540 MeV and with a strange quark mass ${m}_{s}$ close to its physical value. We utilize the all-to-all quark propagator technique to calculate the EM form factors with high precision. Their dependence on ${m}_{s}$ and on the momentum transfer is studied by using the reweighting technique and the twisted boundary conditions for the quark fields, respectively. A detailed comparison with SU(2) and SU(3) ChPT reveals that the next-to-next-to-leading order terms in the chiral expansion are important to describe the chiral behavior of the form factors in the pion mass range studied in this work. We estimate the relevant low-energy constants and the charge radii, and find reasonable agreement with phenomenological and experimental results.

ργ*→π(ρ)transition form factors in the perturbative QCD factorization approach

In this paper, we studied the $\rho \gamma^* \to \pi$ and $\rho\gamma^*\to \rho$ transition processes and made the calculations for the $\rho\pi$ transition form factor $Q^4 F_{\rho\pi}(Q^2)$ and the $\rho$ meson electromagnetic form factors, $F_{\rm LL, LT,TT}(Q^2)$ and $F_{1,2,3}(Q^2)$, by employing the perturbative QCD (PQCD) factorization approach. For the $\rho \gamma^* \to \pi$ transition, we found that the contribution to form factor $Q^4 F_{\rho\pi}(Q)$ from the term proportional to the distribution amplitude combination $\phi^T_{\rho}(x_1)\phi^P_{\pi}(x_2)$ is absolutely dominant, and the PQCD predictions for both the size and the $Q^2$-dependence of this form factor $Q^4 F_{\rho\pi}(Q^2)$ agree well with those from the extended ADS/QCD models or the light-cone QCD sum rule. For the $\rho \gamma^* \to \rho$ transition and in the region of $Q^2\geq 3$ GeV$^2$, further more, we found that the PQCD predictions for the magnitude and their $Q^2$-dependence of the $F_1(Q^2)$ and $F_2(Q^2)$ form factors agree well with those from the QCD sum rule, while the PQCD prediction for $F_3(Q^2)$ is much larger than the one from the QCD sum rule.

Meson electro-magnetic form factors in an extended Nambu–Jona-Lasinio model including heavy quark flavors

Based on an extended NJL model including heavy quark flavors, we calculate the form factors of pseudo-scalar and vector mesons. After taking into account the vector-meson-dominance effect, which introduces a form factor correction to the quark vector coupling vertices, the form factors and electric radii of π+ and K+ pseudo-scalar mesons in the light flavor sector fit the experimental data well. The magnetic moments of the light vector mesons ρ+ and K*+ are comparable with other theoretical calculations. The form factors in the light-heavy flavor sector are presented to compare with future experiments or other theoretical calculations.

Constraining scenarios of the soft/hard transition for the pion electromagnetic form factor with expected data of 12 GeV Jefferson Lab experiments and of the electron-ion collider

It has been shown previously [S. V. Troitsky and V. E. Troitsky, Phys. Rev. D 88, 093005 (2013)] that a nonperturbative relativistic constituent-quark model for the $\ensuremath{\pi}$-meson electromagnetic form factor allows for a quantitative description of the soft/hard transition, resulting in the correct quantum-chromodynamical asymptotics, including normalization, from the low-energy data without further parameter tuning. This happens universally whenever the constituent-quark mass is switched off. The energy range where the transition happens is therefore determined by the quark-mass running at intermediate energies and is not tightly constrained theoretically. Here we consider possible ways to pin down this energy range with coming experimental data. We demonstrate that expected experimental uncertainties of the 12 GeV Jefferson Lab data are larger than the span of predictions of the model, so these data might be used for testing the model but not for determination of the soft/hard transition scale. Contrarily, the projected electron-ion collider will be capable of pinning down the scale.

Meson electromagnetic form factors

The electromagnetic structure of the pseudoscalar meson nonet is completely described by the sophisticated Unitary&Analytic model, respecting all known theoretical properties of the corresponding form factors.

πandρmesons, and their diquark partners, from a contact interaction

We present a unified Dyson-Schwinger equation treatment of static and electromagnetic properties of pseudoscalar and vector mesons, and scalar and axial-vector diquark correlations, based upon a vector-vector contact-interaction. A basic motivation for this study is the need to document a comparison between the electromagnetic form factors of mesons and those diquarks which play a material role in nucleon structure. This is an important step toward a unified description of meson and baryon form factors based on a single interaction. A notable result, therefore, is the large degree of similarity between related meson and diquark form factors. The simplicity of the interaction enables computation of the form factors at arbitrarily-large spacelike-Q^2, which enables us to expose a zero in the rho-meson electric form factor at z_Q^\rho ~ Sqrt[6] m_\rho. Notably, r_\rho*z_Q^\rho ~ r_D*z_Q^D, where r_\rho, r_D are, respectively, the electric radii of the rho-meson and deuteron.

Lattice computations of the pion form factor

We report on a program to compute the electromagnetic form factors of mesons. We discuss the techniques used to compute the pion form factor and present results computed with domain wall valence fermions on MILC asqtad lattices, as well as with Wilson fermions on quenched lattices. The methods can easily be extended to rho-to-gamma-pi transition form factors.

Mesonic form factors

We have started a program to compute the electromagnetic form factors of mesons. We discuss the techniques used to compute the pion form factor and present preliminary results computed with domain wall valence fermions on MILC asqtad lattices, as well as Wilson fermions on quenched lattices. These methods can easily be extended to rho-to-gamma-pi transition form factors.

Calculation of kaon electromagnetic form factor

The kaon meson electromagnetic form factor is calculated in the framework of coupled Schwinger-Dyson and Bethe-Salpeter formulation in simplified impulse approximation (dressed vertex) with modified flat-bottom potential, which is a combination of the flat-bottom potential taking into consideration the infrared and ultraviolet asymptotic behaviours of the effective quark-gluon coupling. All the numerical results give a good fit to experimental values.

Calculation of the π Meson Electromagnetic Form Factor

The modified flat-bottom potential (MFBP) is given by the combination ofthe flat-bottom potential with considerations for the infrared andultraviolet asymptotic behaviour of the effective quark-gluon coupling.The π meson electromagnetic form factor is calculated in theframework of the coupled Schwinger-Dyson equation and the Bethe-Salpeterequation in the simplified impulse approximation (dressed vertex)with the MFBP. All our numerical results give a good fit toexperimental values.

The quark-photon vertex and meson electromagnetic form factors

The ladder Bethe-Salpeter solution for the dressed photon-quark vertex is used to study the low-momentum behavior of the pion electromagnetic and the $\gamma^\star \pi^0 \gamma$ transition form factors. With model parameters previously fixed by light meson masses and decay constants, the low-momentum slope of both form factors is in excellent agreement with the data. In comparison, the often-used Ball-Chiu Ansatz for the vertex is found to be deficient; less than half of the obtained $r_\pi^2$ is generated by that Ansatz while the remainder of the charge radius could be attributed to the tail of the $\rho$ resonance.