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Form factors of the isovector scalar current and the ηπ scattering phase shifts

Abstract : A model for S-wave $\eta\pi$ scattering is proposed which could be realistic in an energy range from threshold up to above one GeV, where inelasticity is dominated by the $K\bar{K}$ channel. The $T$-matrix, satisfying two-channel unitarity, is given in a form which matches the chiral expansion results at order $p^4$ exactly for the $\eta\pi\to\eta\pi$, $\eta\pi\to K\bar{K}$ amplitudes and approximately for $K\bar{K}\to K\bar{K}$. It contains six phenomenological parameters. Asymptotic conditions are imposed which ensure a minimal solution of the Muskhelishvili-Omn\`es problem, thus allowing to compute the $\eta\pi$ and $K\bar{K}$ form factor matrix elements of the $I=1$ scalar current from the $T$-matrix. The phenomenological parameters are determined such as to reproduce the experimental properties of the $a_0(980)$, $a_0(1450)$ resonances, as well as the chiral results of the $\eta\pi$ and $K\bar{K}$ scalar radii which are predicted to be remarkably small at $O(p^4)$. This $T$-matrix model could be used for a unified treatment of the $\eta\pi$ final-state interaction problem in processes such as $\eta'\to \eta \pi\pi$, $\phi\to\eta\pi\gamma$, or the $\eta\pi$ initial-state interaction in $\eta\to3\pi$.
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Contributor : Sophie Heurteau <>
Submitted on : Tuesday, September 29, 2015 - 5:27:03 PM
Last modification on : Monday, June 29, 2020 - 6:24:23 PM

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M. Albaladejo, B. Moussallam. Form factors of the isovector scalar current and the ηπ scattering phase shifts. European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2015, 75 (10), pp.488. ⟨10.1140/epjc/s10052-015-3715-z⟩. ⟨in2p3-01206938⟩



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