[en] The effect of two-rho exchange to the pion-nucleon scattering lengths is calculated to leading order in m_π. It is shown that the contribution to a⁺ and a^- is of order m²_π and m³_π, respectively. (author)

[en] Strong decays of vector mesons above 1 GeV are discussed in the framework of the quark model. A scenario is proposed to resolve the situation with branching ratios by means of the concept of q²q² states coupled to qantiq mesons. The branching ratios of ρ(1450) and ρ(1700) as well as ρ₁(1270) and C(1480) may be qualitatively explained in the presented picture

[en] The interpretation of the enhancement of the electric dipole sum rule due to the ρ exchange potential in terms of virtual ρ photoproduction is discussed. In deriving the ρ photoproduction amplitude, it is shown that invariance under local gauge transformations of the SU(2) x U(1) (isospin x hypercharge) group necessary for a unitary theory, requires a Higgs mechanism to generate the ρ masses. In such a scheme which intrinsically connects on the electromagnetic and strong interactions, linking part of the NN potential to the electromagnetic properties of hadrons, the vector meson dominance prescriptions automatically result, universality is explained and the desired ρ photoproduction amplitude is obtained. In addition 'genuine' three-body ρρρ forces originating from the non-Abelian structure of the group are predicted. (author)

[en] Preliminary results are presented from an analysis of the π⁺π^- system produced in the reaction Κ^-p → π⁺π^- Λ at 11 GeV/c observed with the LASS spectrometer at SLAC. A clear ρ --- ω interference effect is observed, and a fit to the natural parity exchange mass distribution yields a branching fraction estimate of (1.7 ± 0.5) % for the decay ω →π⁺π^-. An amplitude analysis reveals that the bump in the mass distribution in the vicinity of the f₂(1270) actually contains a significant P-wave component. The mass dependence of the corresponding amplitude and phase is well described by a resonant Breit-Wigner line-shape with mass (1266 ± 14) MeV/c², width (166 ± 35) MeV/c², and estimated elasticity ∼ 5%. The interpretation of this state as the first radial excitation of the ρ(770) is discussed. 15 refs., 5 figs

[en] An account of results obtained on the ρ (1250) along with some theoretical consideration is presented. (author). 31 refs

[en] A global analytic model of a single structure function F_π(t) with an arbitrary number of radially excited rho-states and its application to other physical problems like a determination of ρ'(1250) and ρ''(1600) from data on e⁺e^-→π⁺π^-, the prediction of the P-wave isovector ππ phase shift δ₁¹(t) and the inelasticity in the whole experimentally measurable region and the evolution of two-pion contribution to the muon anomalous magnetic moment, are presented. (M.F.W.)

[en] The analysis is made all existing pion form factor data using a model respecting the fundamental principles, including ρ-(770), ρ'-(1250) and ρ''-(1600) contributions without inelastic effects and only depending on physical parameters. The comparison of the obtained results with a previous analysis performed by means of a model with only ρ-(770) and ρ''-(1600) contributions and inelastic effects confirmes the conclusions of the Novosibirsk experimental group that the ρ'-(1250) contribution and inelastic effects in e⁺e^-→π⁺π^- are indistinguishable. However, theoretically predicted behaviours of the P-wave isovector ππ phase shift and the inelasticity from both models and their comparison with the existing data unambiguously favour the model with ρ-(770), ρ''-(1600) and inelastic contributions. (author). 1 fig., 1 tab., 35 refs

[en] We present new results from the DM2 experiment on the η_c-state and the pseudoscalar production seen at the threshold of the vector-vector radiative decays at J/Ψ. The η_c shows a vector-vector dominance in its decays and has a decay pattern which follows the SU(3)F symmetry prediction, this being in contradiction with previous measurements. New pseudoscalar states are clearly present in the invariant mass spectrum of ρ⁰ρ⁰. There are at least three different resonances, here named L₁, L₂, L₃ to underline a supposed common origin. These states have no direct interpretation in the usual qantiq model and they are believed to have an isoscalar nature. An interesting new upper limit on the gT's(2000(division)2500 MeV/c²) production at J/Ψ is given as a by-product of the ρ⁰ρ⁰ analysis

[en] We report the results of a study of inclusive ρ⁰- and f₂-meson production in π^-p interactions at 360 GeV/c obtained in the experiment NA27, using the LEBC/EHS set-up at CERN. The production cross sections for ρ⁰, f₂, and ρ⁰₃ mesons are determined for x_F>0, x_F>0.4, and x_F>0.6, respectively. We present also the distributions in the Feynman variable x_F and in the square of the transverse momentum p²_T for inclusive ρ⁰- and f₂-meson production

[en] Final results are presented on J/Ψ→γρ⁰ρ⁰. The multichannel analysis shows a large pseudoscalar contribution which can be fitted with 3 Breit-Wigners and a small background. In this channel are observed η_c and f₁(1285) productions. η_c→ρρ, ωω, ΦΦ, K*antiK* are analysed in the framework of SU(3) and are consistent with nonet symmetry. At last, Vector+Pseudoscalar final states are studied. η and η' wave functions can be saturated by their quark content. The pseudoscalar mixing angle is measured to be-(20.0±1.6)⁰