The kaon electromagnetic form factor is calculated within a light-front constituent quark model (LFCQM). The electromagnetic components of the current are extracted from the Feynman triangle diagram within the light-front approach. We also obtain the electroweak decay constant and the charge radius for the kaon in the light-front approach. In this work, the kaon observables are calculated and a fairly good agreement is obtained with a very higher accuracy when compared with the experimental data.
We use recent data on K^+ -> pi^+ e^+ e^-, together with known values for the pion form factor, to derive experimental values for the kaon electromagnetic form factor for 0 < q^2 < 0.125 (GeV/c)^2. The results are then compared with the predictions of the Vector Meson Dominance model, which gives a good fit to the experimental results.
We use the Cottingham method to calculate the pion and kaon electromagnetic mass differences with as few model dependent inputs as possible. The constraints of chiral symmetry at low energy, QCD at high energy and experimental data in between are used in the dispersion relation. We find excellent agreement with experiment for the pion mass difference. The kaon mass difference exhibits a strong violation of the lowest order prediction of Dashen's theorem, in qualitative agreement with several other recent calculations.
In kaon decay, electromagnetic radiative corrections can generate shifts in the apparent Delta I = 3/2 amplitude of order alpha A_0/A_2 ~ 22 alpha. In order to know the true Delta I = 3/2 amplitude for comparison with lattice calculations and phenomenology, one needs to subtract off this electromagnetic effect. We provide a careful estimate of the electromagnetic shift in the amplitude, which shows that it is smaller than naive expectations, with a fractional shift of delta A_2/A_2 = -0.016 +- 0.01.
We have applied the light-front formalism to calculate the electromagnetic form factors for the pion and the kaon from two models at low and high energies in order to explore the differences between such models. We have also compared the results for the ratio $F_{K}(Q^2)/F_π(Q^2)$ with the experimental data up to 10 [GeV/c]$^2$ and we have observed that the theoretical results are in good concordance for low energies, but they are very different at higher energy scales.
A combined analysis of the electromagnetic pion and kaon form factors in the neighborhood of J/psi and psi(2S) and of the strong decay amplitude of these resonances into kaons is presented. In the presence of a large relative phase between strong and electromagnetic resonance amplitudes the branching ratio, as measured in electron-positron annihilation, receives an additional contribution from the interference between resonance and continuum amplitude neglected in earlier papers. Our study is model independent and does not rely on the SU(3) symmetry assumptions used in earlier papers. We note …
We use recent data on K^+ -> pi^+e^+e^-, together with known values for the pion form factor, to derive the kaon electromagnetic form factor for 0 <q^2 <0.125 (GeV/c)^2. The results are then compared with predictions of the Linear sigma Model, a quark-triangle model and Vector Meson Dominance. The first two models describe the data at least qualitatively, but the simple Vector Meson Dominance picture gives a detailed quantitative fit to the experimental results.
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.
The electromagnetic form factor is extracted from both components of the electromagnetic current: J(plus) and J(minus) with a pseudo-scalar coupling of the quarks to the kaon. In the case of J(plus) there is no pair term contribution in the Drell-Yan frame. However, J(minus) component of the electromagnetic current the pair term contribution is different from zero and is necessary include it to preserve the rotational symmetry of the current.
A simultaneous investigation of the space- and time-like electromagnetic form factors of the charged kaon is presented within the framework of light-cone QCD, with perturbative $k_T$-factorization including Sudakov suppression. The effects of power suppressed sub-leading twists and the genuine ``soft'' QCD corrections turn out to be dominant at low- and moderate-energies/momentum transfers $Q^2$. Our predictions agree well with the available moderate-energy experimental data, including the recent results from the CLEO measurements and certain estimates based on the phenomenological analyses of…
We investigate the pion and kaon (pi^+, K^+, K^0) electromagnetic form factors in the space-like region: Q^2 ~< 1 GeV, based on the gauged low-energy effective chiral action from the instanton vacuum in the large N_c limit. Explicit flavor SU(3) symmetry breaking is taken into account. The nonlocal contributions turn out to be crucial to reproduce the experimental data. While the pion electromagnetic form factor is in good agreement with the data, the kaon one seems underestimated. We also calculate the electromagnetic charge radii for the pion and kaon: <r^2>_{pi^+}=0.455 fm^2, <r^2>_{K^+}=0.…
We investigate the form factors and decay rates for the semileptonic decays of the kaon($K_{l3})$ using the light-front quark model. The form factors $f_{\pm}(q^{2})$ are calculated in $q^{+}=0$ frame and analytically continued to the time-like region, $q^{2}>0$. Our numerical results for the physical observables, $f_{-}/f_{+}|_{q^{2}=m^{2}_{l}}=-0.38$, $λ_{+}=0.025$(the slope of $f_{+}$ at $q^{2}=m^{2}_{l}$), $Γ(K^{0}_{e3})=(7.30\pm 0.12)\times10^{6}s^{-1}$, and $Γ(K^{0}_{\mu3})=(4.57\pm0.07)\times10^{6}s^{-1}$ are quite comparable with the experimental data and other theoretical model calcul…
We study the electromagnetic form factor of the pion and kaons at low-energies with the use of Chiral Perturbation Theory. The analysis is performed within the three flavour framework and at next-to-next-to-leading order. We explain carefully all the relevant consistency checks on the expressions, present full analytical results for the pion form factor and describe all the assumptions in the analysis. From the phenomenological point of view we make use of our expression and the available data to obtain the charge radius of the pion obtaining $<r^2 >_V^π=(0.452+-0.013) fm^2$, as well as the lo…
We investigate the two-particle twist-3 distribution amplitudes (DAs) of the pseudoscalar mesons, in particular pseudoscalar ($ϕ^P_{3;M}(x)$) and pseudotensor ($ϕ^σ_{3;M}(x)$) DAs of the pion and kaon, in the light-front quark model based on the variational principle. We find that the behavior of the conformal symmetry in each meson distribution amplitude depends on the chiral limit characteristics of the light-front trial wave function taken in the variational principle. We specifically take the two different light-front trial wave functions, Gaussian vs. power-law type, and discuss their cha…
We present a systematical study on the kaon electromagnetic form factors $F_{K^{\pm},K^0,\bar{K}^0}(Q^2)$ within the $k_T$ factorization formalism, where the transverse momentum effects, the contributions from the different helicity components and different twist structures of the kaon light-cone (LC) wave function are carefully analyzed for giving a well understanding of the hard contributions at the energy region where pQCD is applicable. The right power behavior of the hard contribution from the higher helicity components and from the higher twist structures can be obtained by keeping the $…
New, accurate measurements of the pion and kaon electromagnetic form factors are expected in the near future from experiments at electron-positron colliders,using the radiative return method. We construct a model for the timelike pion electromagnetic form factor, that is valid also at momentum transfers far above the $ρ$ resonance. The ansatz is based on vector dominance and includes a pattern of radial excitations expected from dual resonance models.The form factor is fitted to the existing data in the timelike region, continued to the spacelike region and compared with the measurements there…
The unknown constants in Chiral Perturbation Theory needed for an all orders analysis of the polarizabilities and electromagnetic corrections to the masses of the pseudo-Goldstone bosons are estimated at leading order in $1/N_c$. We organize the calculation in an $1/N_c$-expansion and separate long- and short-distance physics contributions by introducing an Euclidean cut-off. The long-distance part is evaluated using the ENJL model and the short-distance part using perturbative QCD and factorization. We obtain very good matching between both. We then include these estimates in a full Chiral Pe…
We calculate the pion and kaon electromagnetic form factors in finite volume for a generic momentum transfer in space-like region, using SU(3) chiral perturbation theory. To this end, we first find the hadronic matrix element in a new form which is suitable for our calculation in finite volume. We present our numerical findings for the chiral behavior and finite volume corrections and compare these for pion and kaon form factors. As a result, for the pion electromagnetic form factor we find the finite volume correction $ΔF^π_{em} = 0.0041$ at momentum transfer $q^2 = -0.1358$ and for the kaon …
We analyze the electromagnetic pion and kaon form factor by including radiative and higher-twist effects within the framework of resummed pQCD in the space-like region. We focus on the transition from the perturbative to non-perturbative behavior in the phenomenological intermediate energy regime. Using a modified k_T factorization scheme with transverse degrees of freedom, we evaluate the non-perturbative soft contributions as distinct from the hard contributions, ensuring no double counting via the Ward identity at Q^2=0. The soft contributions are obtained via local quark-hadron duality whi…
We compute the distribution amplitudes of the pion and kaon in the light-front constituent quark model with the symmetric quark-bound state vertex function. In the calculation we explicitly include the flavor-SU(3) symmetry breaking effect in terms of the constituent quark masses of the up (down) and strange quarks. To calculate the kaon parton distribution functions~(PDFs), we use both the conditions in the light-cone wave function, i.e., when $\bar{s}$ quark is on-shell, and when $u$ quark is on-shell, and make a comparison between them. The kaon PDFs calculated in the two different conditio…
Numerical calculations are performed and compared to the experimental data for the electromagnetic form factor of the kaon, which is extracted from both components of the electromagnetic current, $J^{+}$ and $J^{-}$, with a pseudo-scalar coupling of the quarks to the kaon. In the case of $J^{+}$ there is no pair term contribution in the Drell-Yan frame ($q^{+}=0$). However, for $J^{-}$, the pair term contribution is different from zero and necessary in order to preserve the rotational symmetry of the current. The free parameters are the quark masses and the regulator mass.
We investigate the parton distribution functions (PDFs) of the pion and the kaon by combining quantum chromodynamics (QCD) evolution with the basis light front quantization. The initial PDFs result from the light front wave functions obtained by diagonalizing the effective Hamiltonian consisting of the holographic QCD confinement potential, a complementary longitudinal confinement potential, and the color-singlet Nambu--Jona-Lasinio interactions. The valence-quark PDF of the pion, after QCD evolution, is consistent with the result from the E-0615 experiment at Fermilab. Meanwhile, the pion str…
Kaon T-even transverse-momentum-dependent distributions and form factors in a self-consistent light-front quark model
Inha University（仁荷大学）；Kyungpook National University（庆北国立大学）；The University of Osaka（大阪大学）；Japan Atomic Energy Agency (JAEA)（日本原子力机构）；North Carolina State University（北卡罗来纳州立大学）
We compute the electromagnetic charged kaon form factor in the time-like region by employing a Poincaré covariant formalism of the Bethe-Salpeter equation to study quark-antiquark bound states in conjunction with the Schwinger-Dyson equation for the quark propagator. Following a recent kindred calculation of the time-like electromagnetic pion form factor, we include the most relevant intermediate composite particles permitted by their quantum numbers in the interaction kernel to allow for a decay mechanism for the resonances involved. This term augments the usual gluon mediated interaction bet…
The higher-twist (HT) contribution to the charged kaon pair production in the high energy proton-antiproton collisions at large transverse momentum $p_T$ is investigated by using the frozen coupling constant approach for various kaon distribution amplitudes (DAs), which are predicted by light-cone formalism, the light-front quark model, the nonlocal chiral quark model and the light-front holographic AdS/CFT approach. In the numerics the dependencies of the HT contribution on the transverse momentum $p_T$, the rapidity $y$, and the variable $x_T$ are discussed with special emphasis put on DAs. …
Kaon photo- and electroproduction off a proton near the production threshold are investigated by utilizing an isobar model. The background amplitude of the model is constructed from Feynman diagrams, whereas the resonance term is calculated by using the multipole formalism. It is found that both pseudoscalar and pseudovector models can nicely describe the available photoproduction data up to W = 50 MeV above the threshold. The Lambda resonance S_{01}(1800) is found to play an important role in improving the model. In the case of double polarization observables Ox and Oz our result corroborates…
In this presentation, we briefly review recent investigations on pion and kaon structures from the instanton vacuum. Starting from the low-energy QCD partition function, we have computed the Gasser-Leutwyler low-energy constants, electromagnetic form factors of the pion and kaon, semileptonic decay form factors of the kaon, and light-cone distribution amplitues of the pion and kaon. The results are in good agreement with the experimental and empirical data.
The spectroscopic parameters as well as electromagnetic form factor of the strange particle kaon are investigated in vacuum and a medium with finite density. The obtained vacuum mass and decay constant, which are consistent with the existing experimental results, are used to extract the $ Q^2 $ dependence of the kaon electromagnetic form factor in the interval $Q^2\in [0,10]$ GeV$^2$ in vacuum. The obtained results at lower and intermediate values of $ Q^2 $ are consistent with the existing experimental data within the presented uncertainties. The $ Q^2 $ behavior of the electromagnetic form f…
Kaon photo- and electroproduction in all six isospin channels are investigated by means of an isobaric model. It is found that existing models can only partially describe the current experimental data. Moreover, the extracted coupling constants are mostly inconsistent with the prediction of SU(3) symmetry or the information from hadronic reactions. In order to further analyze this problem, we introduce a form factor at the hadronic vertices $KNY$ (with $Y=Λ~ \textrm{or}~ Σ$) and study its behavior qualitatively. Our result suggests the need of more accurate experiments, especially in the charg…
Within the framework of light-front field theory, we reassess the electromagnetic form factors of the pion and kaon. Comparison with experiment is made for the full range of momentum transfer, q^2<0, including recent data. The light-front model's single regulator mass, m_R, of the \bar qq bound-state vertex function is initially adjusted to reproduce the weak decay constants, f_π and f_K, and both meson's charge radii, r_π and r_K. We study the behavior of these observables under variation of the quark masses and find an optimized parameter set, m_u=m_d, m_s and m_R, for which they are in sens…
A continuum approach to the kaon and pion bound-state problems is used to reveal their electromagnetic structure. For both systems, when used with parton distribution amplitudes appropriate to the scale of the experiment, Standard Model hard-scattering formulae are accurate to within 25% at momentum transfers $Q^2 \approx 8\,$GeV$^2$. There are measurable differences between the distribution of strange and normal matter within the kaons, e.g. the ratio of their separate contributions reaches a peak value of $1.5$ at $Q^2 \approx 6\,$GeV$^2$. Its subsequent $Q^2$-evolution is accurately describ…
The elementary reaction of kaon exclusive electroproduction on protons has been studied in a broad kinematical range. Data for the calculation of the form factor of the kaon have been taken at different values of the invariant center of mass energy W in the range W=1.8, 1.85, 1.98, 2.08 (GeV), for one value of the transferred 4-momentum Q2=2.35 (GeV/c)2. In this analysis, we calculated sigma-L and sigma-T by using the Rosenbluth separation. Then the electromagnetic kaon form factor was calculated by Chew-Low extrapolation.
We report on the MILC Collaboration calculation of electromagnetic effects on light pseudoscalar mesons. The simulations employ asqtad staggered dynamical quarks in QCD plus quenched photons, with lattice spacings varying from 0.12 to 0.06 fm. Finite volume corrections for the MILC realization of lattice electrodynamics have been calculated in chiral perturbation theory and applied to the lattice data. These corrections differ from those calculated by Hayakawa and Uno because our treatment of zero modes differs from theirs. Updated results for the corrections to "Dashen's theorem" are presente…
The electromagnetic form factors of charged and neutral kaons are strongly constrained by their low-energy singularities, in the isovector part from two-pion intermediate states and in the isoscalar contribution in terms of $ω$ and $ϕ$ residues. The former can be predicted using the respective $ππ\to\bar K K$ partial-wave amplitude and the pion electromagnetic form factor, while the latter parameters need to be determined from electromagnetic reactions involving kaons. We present a global analysis of time- and spacelike data that implements all of these constraints. The results enable manifold…
We investigate the effects of the kaon cloud on the electromagnetic and axial-vector form factors of the $Ω^-$ baryon within the framework of the chiral quark-soliton model. We first derive the profile function of the chiral soliton in such a way that the kaon Yukawa tail is properly produced self-consistently. Then, we compute the electromagnetic form factors of the $Ω^-$ baryon. The results for the electromagnetic form factors are compared with the lattice data. We find that the results with the kaon tail employed are in better agreement with the lattice data, compared with those obtained wi…
The pion and kaon electromagnetic form factors $F_M(Q^2)$ are calculated at the leading order of pQCD using the running coupling constant method. In calculations the leading and next-to-leading order terms in $α_S((1-x)(1-y)Q^2)$ expansion in terms of $α_S(Q^2)$ are taken into account. The resummed expression for $F_M(Q^2)$ is found. Results of numerical calculations for the pion (asymptotic distribution amplitude) are presented.
The recent precise measurements of the $e^+e^-\to K_SK_L$ and $e^+e^-\to K^+K^-$ cross sections and the hadronic spectral function of the $τ^-\to K^-K_Sν_τ$ decay are used to extract the isoscalar and isovector electromagnetic kaon form factors and their relative phase in a model independent way. The experimental results are compared with a fit based on the vector-meson-dominance model.
At large momentum transfers the photon interacts with the charges and spins of the constituent partons in a hadron. It is expected that the neutral kaon can acquire finite electromagnetic form factors because its wave function is affected by the order of magnitude difference between the mass of the strange quark and that of the down quark, or flavor $SU(3)$ breaking. We report on the first measurement of the form factor of neutral kaons at the large timelike momentum transfer of $|Q^2|=17.4$ GeV$^2$ by measuring the cross section for $e^+e^-\to K_SK_L$ at $\sqrt{s}=4.17$ GeV using CLEO-c data …
We analyze the higher-twist effects and the SU(3)-flavour symmetry breaking in the correlation functions used to calculate form factors of pseudoscalar mesons in the QCD light-cone sum rule approach. It is shown that the Ward identities for these correlation functions yield relations between twist-4 two- and three-particle distribution amplitudes. In addition to the relations already obtained from the QCD equations of motions, we have found a new one. With the help of these relations, the twist-4 contribution to the light-cone sum rule for the pion electromagnetic form factor is reduced to a v…
We derive the lowest-order $q\bar q$ valence light-front wave function for the pion with Lz=0 and |Lz|=1, which reproduces its valence parton distribution and the electromagnetic form factor consistent with data.
Using the light-front kaon wave function based on a Bethe-Salpeter amplitude model for the quark-antiquark bound state, we study the Electromagnetic Form Factor (EMFF) of the kaon in nuclear medium within the framework of light-front field theory. The kaon model we adopt is well constrained by previous and recent studies to explain its properties in vacuum. The in-medium kaon EMFF is evaluated for the + component of the electromagnetic current, $J^+$, in the Breit frame. In order to consistently incorporate the constituent up and antistrange quarks of the kaon immersed in symmetric nuclear mat…
Longitudinal and transverse quark momentum distributions in the nucleon are calculated from a phenomenological quark-nucleon vertex function obtained through an investigation of the nucleon electromagnetic form factors within a light-front framework.
A symmetry-preserving regularization procedure for dealing with the contact interaction model is proposed in this work. This regularization procedure follows a series of consistency conditions which are necessary to maintain gauge symmetry. Under this regularization, proofs for the preservation of the Ward-Takahashi identities are given and the loop integrals in the contact interaction model are systematically computed. As an application example, the kaon electromagnetic form factor and $K_{l3}$ transition form factor are computed and self-consistent results are obtained. Since the proposed re…
We compute the matrix elements of the electromagnetic (EM) operator between kaon and pion states, using lattice QCD with maximally twisted-mass fermions and two flavors of dynamical quarks (Nf = 2). The EM operator is renormalized non-perturbatively in the RI'/MOM scheme and our simulations cover pion masses as light as 260 MeV and three values of the lattice spacing, ranging from ~ 0.07 up to ~ 0.1 fm. At the physical point our preliminary result for the K -> pion tensor form factor at zero-momentum transfer is fT[Kπ](0) = 0.42(2_stat), which differs significantly from the old quenched result…
We compute the matrix elements of the electromagnetic (EM) operator (\bar{s} F{μν} σ{μν} d) between kaon and pion states, using lattice QCD with maximally twisted-mass fermions and two flavors of dynamical quarks (Nf = 2). The operator is renormalized non-perturbatively in the RI'/MOM scheme and our simulations cover pion masses as light as 270 MeV and three values of the lattice spacing from ~ 0.07 up to ~ 0.1 fm. At the physical point our result for the corresponding tensor form factor at zero-momentum transfer is fT{Kπ}(0) = 0.417 (14_stat) (5_syst), where the systematic error does not incl…
We investigate the parton distribution functions (PDFs) of the pion and kaon from the eigenstates of a light-front effective Hamiltonian in the constituent quark-antiquark representation suitable for low-momentum scale applications. By taking these scales as the only free parameters, the valence quark distribution functions of the pion, after QCD evolving, are consistent with the E615 experiment at Fermilab. In addition, the ratio of the up quark distribution in the kaon to that in the pion also agrees with the NA3 experimental result at CERN.
Experiments at high luminosity electron-positron colliders allow to study the kaon and the pion form factors in the time-like region up to high energies. Also the kaon and the pion pair production at and around the narrow resonances J/psi and psi(2S) can be investigated, with the interference between electromagnetic and hadronic amplitudes as one of the most interesting phenomenas. Parameterisations of charged and neutral kaon as well as pion form factors, which lead to an improved description of the data in the region of large invariant masses of the meson pair, are presented. They are implem…
Charge symmetry breaking (CSB) effects associated with the $u$ and $d$ quark mass difference are investigated in the quark distribution functions and spacelike electromagnetic form factors of the pion and kaon. We use a confining version of the Nambu--Jona-Lasinio model, where CSB effects at the infrared scale associated with the model are driven by the dressed $u$ and $d$ quark mass ratio, which because of dynamical chiral symmetry breaking is much closer to unity than the associated current quark mass ratio. The pion and kaon are given as bound states of a dressed quark and a dressed antiqua…
The kaon electromagnetic (e.m.) form factor is reviewed considering a light-front constituent quark model. In this approach, it is discussed the relevance of the quark-antiquark pair terms for the full covariance of the e.m. current. It is also verified, by considering a QCD dynamical model, that a good agreement with experimental data can be obtained for the kaon weak decay constant once a probability of about 80% of the valence component is taken into account.
We present the most accurate calculation for the pion and kaon electromagnetic form factors in the framework of perturbative QCD, where the power corrections up to twist-4 of the meson distribution amplitudes and the next-to-leading-order QCD corrections up to subleading power are included. In order to guarantee the gauge invariance of the meson to vacuum matrix element, we take into account both assignments with the lowest Fock state and the high Fock state with an additional valence gluon. Our results confirm the power behaviour of the twist expansion and show the chiral enhancement effect a…
