1,010 research outputs found

    Effective Chiral Lagrangians with an SU(3)-Broken Vector-Meson Sector

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    The accuracy of effective chiral lagrangians including vector-mesons as (hidden symmetry) gauge fields is shown to be improved by taking into account SU(3)-breaking in the vector-meson sector. The masses, MVM_V, and couplings to the photon field and pseudoscalar pairs, fVγf_{V\gamma} and gVPPg_{VPP}, are all consistently described in terms of two parameters, which also fit the values for the pseudoscalar decay-constants, fPf_P, and charge radii, . The description of the latter is further improved when working in the context of chiral perturbation theory.Comment: 10 pages, LaTeX file, A postscript version can be obtained from anonymous ftp at ftp://ftp.ifae.es/preprint.ft/

    Extracting Br(omega->pi^+ pi^-) from the Time-like Pion Form-factor

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    We extract the G-parity-violating branching ratio Br(omega->pi^+ pi^-) from the effective rho-omega mixing matrix element Pi_{rho omega}(s), determined from e^+e^- -> pi^+ pi^- data. The omega->pi^+ pi^- partial width can be determined either from the time-like pion form factor or through the constraint that the mixed physical propagator D_{rho omega}^{mu nu}(s) possesses no poles. The two procedures are inequivalent in practice, and we show why the first is preferred, to find finally Br(omega->pi^+ pi^-) = 1.9 +/- 0.3%.Comment: 12 pages (published version

    New Constraints on Dispersive Form Factor Parameterizations from the Timelike Region

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    We generalize a recent model-independent form factor parameterization derived from rigorous dispersion relations to include constraints from data in the timelike region. These constraints dictate the convergence properties of the parameterization and appear as sum rules on the parameters. We further develop a new parameterization that takes into account finiteness and asymptotic conditions on the form factor, and use it to fit to the elastic \pi electromagnetic form factor. We find that the existing world sample of timelike data gives only loose bounds on the form factor in the spacelike region, but explain how the acquisition of additional timelike data or fits to other form factors are expected to give much better results. The same parameterization is seen to fit spacelike data extremely well.Comment: 24 pages, latex (revtex), 3 eps figure

    Measurement of the Pion Form Factor in the Energy Range 1.04-1.38 GeV with the CMD-2 Detector

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    The cross section for the process e+eπ+πe^+e^-\to\pi^+\pi^- is measured in the c.m. energy range 1.04-1.38 GeV from 995 000 selected collinear events including 860000 e+ee^+e^- events, 82000 μ+μ\mu^+\mu^- events, and 33000 π+π\pi^+\pi^- events. The systematic and statistical errors of measuring the pion form factor are equal to 1.2-4.2 and 5-13%, respectively.Comment: 5 pages, 2 figure

    A quark model analysis of the charge symmetry breaking in nuclear force

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    In order to investigate the charge symmetry breaking (CSB) in the short range part of the nuclear force, we calculate the difference of the masses of the neutron and the proton, ΔM\Delta {\rm M}, the difference of the scattering lengths of the p-p and n-n scatterings, Δa\Delta a, and the difference of the analyzing power of the proton and the neutron in the n-p scattering, ΔA(θ)\Delta A(\theta), by a quark model. In the present model the sources of CSB are the mass difference of the up and down quarks and the electromagnetic interaction. We investigate how much each of them contributes to ΔM\Delta {\rm M}, Δa\Delta a and ΔA(θ)\Delta A(\theta). It is found that the contribution of CSB of the short range part in the nuclear force is large enough to explain the observed ΔA(θ)\Delta A(\theta), while Δa\Delta a is rather underestimated.Comment: 26 pages,6 figure

    Testing QCD with Hypothetical Tau Leptons

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    We construct new tests of perturbative QCD by considering a hypothetical tau lepton of arbitrary mass, which decays hadronically through the electromagnetic current. We can explicitly compute its hadronic width ratio directly as an integral over the e^+ e^- annihilation cross section ratio, R_{e^+e^-}. Furthermore, we can design a set of commensurate scale relations and perturbative QCD tests by varying the weight function away from the form associated with the V-A decay of the physical tau. This method allows the wide range of the R_{e^+e^-} data to be used as a probe of perturbative QCD.Comment: 4 pages, 4 figure

    The Dipion Mass Spectrum In e+e- Annihilation and tau Decay: A Dynamical (rho0, omega, phi) Mixing Approach

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    We readdress the problem of finding a simultaneous description of the pion form factor data in e+e- annihilations and in tau decays. For this purpose, we work in the framework of the Hidden Local Symmetry (HLS) Lagrangian and modify the vector meson mass term by including the pion and kaon loop contributions. This leads us to define the physical rho, omega and phi fields as linear combinations of their ideal partners, with coefficients being meromorphic functions of s, the square of the 4--momentum flowing into the vector meson lines. This allows us to define a dynamical, i.e. s-dependent, vector meson mixing scheme. The model is overconstrained by extending the framework in order to include the description of all meson radiative (V P gamma and P gamma gamma couplings) and leptonic (Ve+e- couplings) decays and also the isospin breaking (omega/ phi --> pi+ pi-) decay modes. The model provides a simultaneous, consistent and good description of the e+e- and tau dipion spectra. The expression for pion form factor in the latter case is derived from those in the former case by switching off the isospin breaking effects specific to e+e- and switching on those for tau decays. Besides, the model also provides a good account of all decay modes of the form V P gamma, Pgamma gamma as well as the isospin breaking decay modes. It leads us to propose new reference values for the rho^0 --> e+ e- and omega --> pi+ pi- partial widths which are part of our description of the pion form factor. Other topics (phi --> K anti K, the rho meson mass and width parameters) are briefly discussed. Therefore, we confirm the 3.3 sigma discrepancy between the theoretical estimate of a_mu based on e+e- and its direct BNL measurement.Comment: 71 pages, 8 figures. Accepted by EPJ C. Version 3: correct minor typos, minor changes spread out into the text. Extension of Sections 12.2 and 12.3.5 and introduction of the new Appendix

    Pion and Kaon Vector Form Factors

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    We develop a unitarity approach to consider the final state interaction corrections to the tree level graphs calculated from Chiral Perturbation Theory (χPT\chi PT) allowing the inclusion of explicit resonance fields. The method is discussed considering the coupled channel pion and kaon vector form factors. These form factors are then matched with the one loop χPT\chi PT results. A very good description of experimental data is accomplished for the vector form factors and for the ππ\pi\pi P-wave phase shifts up to s1.2\sqrt{s}\lesssim 1.2 GeV, beyond which multiparticle states play a non negligible role. In particular the low and resonance energy regions are discussed in detail and for the former a comparison with one and two loop χPT\chi PT is made showing a remarkable coincidence with the two loop χPT\chi PT results.Comment: 20 pages, 7 figs, to appear in Phys. Rev.
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