Masses and couplings of vector mesonsfrom the pion electromagnetic,weak, and $\pi\gamma$ transition form factors期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

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Masses and couplings of vector mesonsfrom the pion electromagnetic,weak, and $\pi\gamma$ transition form factors

Authors:	Email author" target="_blank">D?Melikhov Email author O?Nachtmann V?Nikonov T?Paulus

Institution:	(1) Institut für Theoretische Physik, Philosophenweg 16, 69120 Heidelberg, Germany;(2) Petersburg Nuclear Physics Institute, 188300 Gatchina, St.-Petersburg, Russia

Abstract:	We analyze the pion electromagnetic, charged-current, and $\pi\gamma$ transition form factors at timelike momentum transfers q, $q^2 = s\le 1.4$ GeV², using a dispersion approach. We discuss in detail the propagator matrix of the photon-vector meson system and define certain reduced amplitudes, or vertex functions, describing the coupling of this system to final states. We then apply the derived analytic expressions to the analysis of the recent $e^ + e^-\to \pi^ + \pi^-$ , $\tau^-\to \pi^-\pi^0\nu_\tau$ , and $e^ + e^-\to \pi^0\gamma$ data. We find the reduced amplitudes for the coupling of the photon and vector mesons to two pseudoscalars to be constant, independent of s, in the range considered, indicating a freezing of the amplitudes for $s\le 1$ GeV. The fit to the form factor data leads to the following values of the Breit-Wigner resonance masses $m_{\rho^-} = 775.3\pm 0.8$ MeV, $m_{\rho^0} = 773.8\pm 0.6$ MeV and $m_\omega = 782.43\pm 0.05$ MeV, where the errors are only statistical.Received: 8 December 2003, Published online: 23 March 2004T. Paulus: Now at Philips

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