Decay constant ratios ƒ ηc/ƒ J/ψ and ƒ ηb/ƒ ψ

We calculate the decay constant ratios ? _ηc/? _J/ψ and ? _ηb/? _ψ. In the calculation we take into account the mock meson structures of the mesons, as well as the difference of the wave functions at origin of the vector and pseudoscalar mesons studied by Ahmady and Mendel. We find that the different spin structures of the mesons much affect the ratios. We incorporate our results in the prediction of the branching ratios of B → K η _c.     

Tri-meson mixing of π–η–η′ and ρ–ω–φ in the light-cone quark model

The radiative transition form factors of the pseudoscalar mesons π, η, η′ and the vector mesons ρ, ω, φ are restudied with π–η–η′ and ρ–ω–φ in the tri-meson-mixing pattern, which is described by tri-mixing matrices in the light-cone constituent quark model. The experimental transition decay widths are better reproduced with tri-meson mixing than previous results in a two-mixing-angle scenario of only two-meson η–η′ mixing and ω–φ mixing.     

A Modified Pion-Rho-Omega Mesonic Lagrangian in Nuclear Matter

We present an in-medium modified effective Lagrangian which describes the pion, rho- and omega mesons and the corresponding soliton properties in nuclear matter. We discuss possible modifications of ρ- and ω-meson properties in nuclear matter. In particular, the masses of vector mesons are shown to decrease about 30% at normal nuclear matter density within the present approach.     

Single meson photoproduction and IR renormalons

Single pseudoscalar and vector mesons hard semi-inclusive photoproductionγh → MX via higher twist mechanism is calculated using the QCD running coupling constant method. It is proved that in the context of this method a higher twist contribution to the photoproduction cross section cannot be normalized in terms of the meson electromagnetic form factor. The structure of infrared renormalon singularities of the higher twist subprocess cross section and the resummed expression (the Borel sum) for it are found. Comparisons are made with earlier results, as well as with leading twist cross section. Phenomenological effects of studied contributions for π,K,?-meson photoproduction are discussed.     

Masses and electroweak properties of light mesons in the relativistic quark model

The masses, pseudoscalar and vector weak decay constants and electromagnetic form factors of light S-wave mesons are studied in the framework of the relativistic quark model based on the quasipotential approach. We use the same model assumptions and parameters as in our previous investigations of heavy meson and baryon properties. The masses and wave functions of the ground state and radially excited π, ρ, K, K^* and φ mesons, obtained by solving numerically the relativistic Schrödinger-like equation with the complete relativistic qq? potential including both spin-independent and spin-dependent terms, are presented. Novel relativistic expressions for the weak decay constants of the pseudoscalar and vector mesons are derived. It is shown that the intermediate negative-energy quark states give significant contributions which essentially decrease the decay constants bringing them in agreement with experimental data. The electromagnetic form factors of the pion, charged and neutral kaon are calculated in a broad range of the space-like momentum transfer. The corresponding charge radii are determined. All results agree well with the available experimental data.     

Production of P-wave charmonium states in two-particle decays of B c mesons

On the basis of the model of hard one-gluon exchange, the two-particle hadronic decays of B _c mesons into S-and P-wave charmonium states, B _c → X _cc π(ρ), are considered at high momentum transfers and in the nonrelativistic approximation. It is shown that the width with respect to B _c-meson decay into S-wave charmonium states is two times greater than the width with respect to B _c-meson decay into P-wave states and that the yield of J/ψ mesons in the cascade processes of B _c-meson decay via the formation and radiative decay of P-wave charmonium states is approximately 8% of the yield of directly produced J/ψ mesons.     

A relativistic quark model for mesons based on numerical solutions of the Bethe-Salpeter equation

A study is made to determine if the results of the nonrelativistic quark model can be reproduced by a fully relativistic model of deeply bound $\text{spin}\text{-}\text{1}\text{2}$ quarks. It is found that the relativistic model does not reproduce the nonrelativistic results, even when the quarks have nonrelativistic momenta. However, the model is rather successful in accounting for the known properties of mesons.Numerical solutions to the Bethe-Salpeter equation are obtained for pseudoscalar and vector bound states of equal mass quark-antiquark pairs, with either a scalar, pseudoscalar, or neutral vector exchange interaction. The interaction function corresponds to single particle exchange, with the addition of either one or two regulating terms. It is found that the second regulator allows the internal quark momentum to be nonrelativistic, but that the spinor structure of the wave function remains highly relativistic.Only the scalar interaction can account for the observed spectrum of states. The pseudoscalar interaction yields a vector state of lower mass than the pseudoscalar state, and the vector interaction leads to a vector state which lies approximately one quark mass above the pseudoscalar state. The λ quark is taken as slightly heavier than the p and n, and the perturbation treatment of the mass difference leads to a quadratic mass formula.The decay amplitudes for π, K → μν are calculated, and it is found, independent of parameters, that $\text{?}{}_{\mathrm{\pi }}\text{≈ ?}{}_{\mathrm{K}}$ for either a scalar or vector interaction, in agreement with experiment and in contrast with the nonrelativistic model. The amplitudes for ?^o, ω, φ → e⁺e^?, μ⁺μ^? are also calculated, but in this case the ratios (again parameter independent) are in minor discrepancy with experiment.The question of the additivity of quark amplitudes is examined by calculating (with significant restrictions) the magnetic moments of the vector mesons and the amplitudes for magnetic transitions such as ω → π^oγ. The magnetic moments of the vector mesons have the same (trivial) ratios to each other as in the nonrelativistic model, but they are strongly enhanced over the sum of the quark magnetic moments. The amplitude for magnetic transitions, however, is related to the quark magnetic moments in approximately the same ratio as in the nonrelativistic model.The model is also used to obtain parameter dependent predictions for the masses and decay amplitudes. These predictions are not experimentally correct, but are generally well within an order of magnitude for a wide range of the parameters.The most significant defect discovered of the model is the presence of ghost states (the daughters of the vector mesons, with J^PC = 0^+?) with masses of about 2 BeV.     

Hadronic three-body decays of light vector mesons

The decays of light vector mesons into three pseudoscalar mesons are calculated to leading order in the recently proposed counting scheme that is based on the hadrogenesis conjecture. Fully differential as well as integrated decay widths are presented. Since the required parameters have been fixed by other processes, the considered three-body decays are predictions of the presented approach. The decay width of the omega meson into three pions agrees very well with the experiment. The partial decay widths of the K^* into its three K channels are predicted.     

The radial excitations of η−η′ mesons

The possibility of identification of a number of the recently discoveredJ ^PC=0^?+ isosinglet resonances (the ζ(1275), ι(1460) and others) as radial excitations of the η(549)- and η′(958)-mesons is investigated within the earlier developed phenomenological approach to analyse radial excitations of light mesons. The widths of the electromagnetic and strong decays of these mesons and the branching ratios of their production in the radiativeJ/ψ decay, as well as in the π^- p charge exchange reaction, are estimated. It is pointed out that the abundant production of the ι-meson in theJ/ψ-decays and the small width of the ι→2γ decay put forward repeatedly as an evidence for the glueball nature of this meson, can qualitatively be obtained in one of the considered schemes of the radial excitations of the η?η′-system.     

Radiative leptonic decays of pseudoscalar mesons in the bilocal relativistic potential model

Radiative leptonic decays of the pseudoscalar mesons are studied in the bilocal relativistic potential model. Partial and total widths of the pion decay are calculated. It is shown that, in the model under consideration, the decay widths can be determined by calculating the vector (f _v ) and axial-vector (f _a ) form factors. These form factors can be found by jointly solving the Salpeter and Schwinger-Dyson equations with a specified interquark potential.     

τ− → π−π0ντ decay in the extended NJL model

The width of the decay τ^? → π^?π⁰ν_τ was calculated in the extended NJL model. Contact interaction of W boson with a pion pair as well as the contribution of the ρ mesons in the ground and first radialexcited states are taken into account. The sum of the contact diagram and diagram with intermediate ρ meson in the ground state leads to the result which coincides with the result of the vector-dominance model. Our results are in satisfactory agreement with experimental data.     

Constituent quarks,soft pions and meson masses

In the constituent quark model, a simple mass formula is given to relate the masses of the vector and pseudoscalar mesons. Good agreement is obtained for all mesons, from the lightest π, ? mesons to the heaviest. In the limit of vanishing pion mass, alower limit of 230 MeV is obtained for the constituent quark mass.     

Effect of the a 1(1260) resonance on the ρ → 4π and ω,ø → 5 π decay widths

The contribution of the a ₁(1260) meson to the ρ(770) → 4π,ω(782) → 5π, and ø(1020) → 5π decay amplitudes is analyzed on the basis of the chiral model of pseudoscalar, vector, and axial-vector mesons that is based on generalized hidden local symmetry and which is supplemented with terms induced by the Wess-Zumino anomaly. It is shown that the intensities of the above decays are enhanced upon taking into account the a ₁ meson in intermediate states. For the a ₁-meson mass $m_{a_1 } $ varying from 1.23 GeV to $m_p \sqrt 2 = 1.09 GeV$ , the enhancement factor grows from 1.3 to 1.9.     

Influence of absorption on peripheral photoproduction of vector mesons

Photoproduction ofρ andω mesons on nucleons is considered in the peripheral model. The interaction mechanism is assumed to be pseudoscalar and scalar exchange. Absorptive final-state interactions are taken into account. The differential cross section and the angular distribution for the decay are calculated and compared with experimental data.     

Perturbative QCD and the exclusive decay of heavy quarkonium into a photon and two mesons

We consider the radiative decays of the ³S₁ ground state Q$\text{Q}$ into a real photon and two light pseudoscalar or vector mesons. For sufficiently large mass of the heavy quark Q, the decay, e.g. ? → γππ, can be calculated in perturbative QCD, provided that the photon does not carry away a predominant fraction of the available energy. We present differential and integrated Dalitz plot distributions and, for quarkonium states produced with transverse polarization in e⁺e^? annihilation, angular distributions of the orientation of the decay triangle relative to the beam direction.     

Radiative decays of vector mesons in the chiral bag model

A new model of radiative -meson decays of vector mesons in the chiral bag model is proposed. The quark--meson interaction has the form of a pseudoscalar coupling and is located on the bag surface. The vector meson decay width depends on the quark masses, the -meson decay constant, the radius of the bag, and the free parameter Z², which specifies the disappearance of the bag during the decay. The obtained results for the -and p-decay widths are in satisfactory agreement with the experiment.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 71–76, February, 1988.     

Width of the ? meson in nuclear matter

The ratios of the cross sections for ?-meson production induced by 2.83-GeV protons on Cu, Ag, and Au nuclei to the respective cross section for C nuclei were measured at the ANKE-COSY facility in the momentum range of 0.6?C1.6 GeV/c and the angular range of 0°?C8°. The product ? mesons were identified by their decay ? ?? K ⁺ K ^?. The procedure used to separate kaon pairs was described in detail, and all sources of the background and their contribution to the resulting error in the values found for the above cross-section ratios were analyzed. The A dependence of the cross section for ?-meson production was shown to obey the A ^0.56±0.03 law. The total width of the ? meson at a normal nuclear density was extracted from a comparison of the measured cross-section ratios with the results of calculations based on two theoretical models. The resulting width value exceeds substantially both the vacuum width and the width expected in the absence of the nuclear-matter effect on the properties of the ? meson.     

(η−η′−ι)-mixing,decay and production mechanisms

We present a phenomenological model for meson-glueball mixing and apply it to the mixing of the pseudoscalar mesons η and η′ with the ι(1440)-particle as the prime candidate for a 0^?+-glueball. Using the MIT bag model framework, our model incorporates, among other elements, configuration mixing effects due to virtually excited states, as well as mixing of quark and gluon components. We evaluate the portions of quark antiquark and two-gluon admixtures in η,η′ and ι. The results are used to study various decay and production processes involving these particles. In particular, we calculate the radiative and the 2γ-decay widths of the light mesons and make predictions for the widths of the ι in these channels. Furthermore, production mechanisms of the light mesons in electromagnetic and hadronicJ/ψ-decays are used to evaluate the branching ratios for the production of the ι in variousJ/ψ-transitions. Our results are generally in reasonable agreement with experimental data. Especially we predict a rather large width for the decay ι→ργ and a sizable production rate for the ι in the transitionJ/ψ→ωι.