Vector to pseudoscalar meson radiative transitions in chiral theory with resonances

The form factor of the vector meson V conversion transition into the pseudoscalar meson Ρ and the lepton pair l⁺l⁻ is presented for V ≡ ρ⁰, ω, φ and Ρ ≡ π⁰, η. Our approach is based on the chiral effective field theory with resonances. The normalized form factor for ω → πγ* transition was fitted to the recent NA 60 data by varying the only free parameter σV. The results are compared to the available data and to the predictions of other models.Формфакторы для конверсионного перехода векторного мезона V в псевдоскалярный мезон Ρ и лептонную пару l⁺l⁻ представлены для случаев V ≡ ρ⁰, ω, φ и Ρ ≡ π⁰, η. Подход основан на эффективной киральной теории поля с резонансами. Нормированный формфактор для перехода ω → πγ* подогнан к данным эксперимента NA 60 при помощи варьирования единственного свободного параметра σV. Результаты подхода сравниваются с имеющимися данными и предсказаниями других моделей.Формфактори для конверсійного переходу векторного мезона V в псевдоскалярний мезон Ρ та лептонну пару l⁺l⁻ представлено для випадків V ≡ ρ⁰, ω, φ і Ρ ≡ π⁰, η. Підхід засновано на ефективній кіральній теорії поля з резонансами. Нормований формфактор для переходу ω → πγ* підігнано до даних експерименту NA 60 за допомогою варіації єдиного вільного параметру σV. Результати підходу порівняно з наявними даними та передбаченнями інших моделей

e+e- annihilation to (pi0 pi0 gamma) and (pi0 eta gamma) as a source of information on scalar and vector mesons

We present a general framework for the model-independent decomposition of the fully differential cross section of the reactions e+e- -> gamma* -> (pi0 pi0 gamma) and e+e- -> gamma* -> (pi0 eta gamma), which can provide important information on the properties of scalar mesons: f0(600), f0(980) and a0(980). For the model-dependent ingredients in the differential cross section, an approach is developed, which relies on Resonance Chiral Theory with vector and scalar mesons. Numerical results are compared to data. The framework is convenient for development of a Monte Carlo generator and can also be applied to the reaction e+e- -> gamma* -> (pi+ pi- gamma).Comment: 15 pages, 12 Figures, 4 Tables; LaTeX svjour style; update to the version accepted for publication in the European Physical Journal

Radiative decays with light scalar mesons and singlet-octet mixing in ChPT

We study different types of radiative decays involving f0(980) and a0(980) mesons within a unified ChPT-based approach at one-loop level. Light scalar resonances which are seen in pi pi, pi eta, K K-bar channels of phi(1020) radiative decays and in J/psi decays are responsible for key questions of low-energy dynamics in the strong interaction sector, and decays phi(1020) -> gamma a0(980), phi(1020) -> gamma f0(980), a0(980) -> gamma gamma, f0(980) -> gamma gamma are of interest for current experimental programs in Juelich, Frascati and Novosibirsk. From theoretical point of view it is important to verify whether light scalar mesons are members of some flavor octet or nonet. We find a value of mixing angle dictated by consistency with experiment and coupling structures of ChPT Lagrangian. Decay widths f0(980)/a0(980) -> gamma rho(770)/omega(782), which are not studied experimentally yet, are predicted. We also obtain several relations between widths, which hold independently of coupling constants and represent a fingerprint of the model.Comment: 18 pages, 8 figures; misprints in text and tables corrected, discussion extended, references added; version accepted for publication in Eur.Phys.J.

ρ0−γ\rho^0 - \gamma mixing in the neutral channel pion form factor Fπ(e)(s)F^{(e)}_{\pi}(s) and its role in comparing e+e−e^+ e^- with τ\tau spectral functions

We study the effect of rho^0-gamma mixing in e^+e^- to pi^+pi^- and its relevance for the comparison of the square modulus of the pion from-factor |F^(e)_pi|^2, as measured in e^+e^- annihilation experiments, and |F^(tau)_pi|^2 the corresponding quantity obtained after accounting for known isospin breaking effects by an isospin rotation from the tau-decay spectra. After correcting the tau data for the missing rho-gamma mixing contribution, besides the other known isospin symmetry violating corrections, the pi pi I=1 part of the hadronic vacuum polarization contribution to the muon g-2 are fully compatible between tau based and e^+e^- based evaluations. tau data thus confirm result obtained with e^+e^- data. Our evaluation based on all e^+e^- data including more recent BaBar and KLOE data yields a_mu^(had)=690.75(4.72) x 10^{-10} (e^+e^- based), while including tau data we find a_mu^(had)=690.96(4.65) X 10^{-10} (e^+e^-+tau based). This backs the ~3 sigma deviation between theory and experiment. For the tau di-pion branching fraction we find B^{CVC}_{pi pi^0}=25.20 \pm0.0.17\pm0.28 from e^+e^-+CVC, while B_{pi pi^0}=25.34\pm0.0.06\pm0.08 is evaluated directly from the tau spectra.Comment: 18 pages, 18 figures, Fig.2 added,Refs. 3,12,14 added, text referring to Refs. 13,14 corrected, typos correcte