The European Physical Journal C

ISSN: 1434-6044 (printed version)
ISSN: 1434-6052 (electronic version)

Table of Contents

Abstract Volume 5 Issue 2 (1998) pp 327-335
DOI 10.1007/s100529800848

theoretical physics:
Flavor symmetry breaking and mixing effects in the $\eta \gamma$ and $\eta'\gamma$ transition form factors

T. Feldmann, P. Kroll

Department of Theoretical Physics, University of Wuppertal, D-42097 Wuppertal, Germany (e-mail: kroll@theorie.physik.uni-wuppertal.de)

Received: 13 November 1997 / Revised version: 13 January 1998 / Published online: 10 March 1998

Abstract. We reanalyze the $\eta\gamma$ and $\eta'\gamma$ transition form factors within the modified hard scattering approach on the basis of new experimental data from CLEO [1] and L3 [2]. Our approach perfectly describes the experimental data over a wide range of the virtuality of the probing photon, 1 GeV$^2\leq Q^2 \leq 15$ GeV$^2$. The analysis provides hints that the conventional flavor octet-singlet scheme for the $\eta$-$\eta'$ mixing is too simple. A more general mixing scheme on the other hand, involving two mixing angles, leads to a very good description of the transition form factors and also accounts for the two-photon decay widths of the $\eta$ and $\eta'$ mesons as well as for the ratio of the widths for the $J/\psi \to \eta'\gamma$ and $J/\psi \to \eta\gamma$ decays. We also investigate the questions of possible deviations of the $\eta$ and $\eta'$ distribution amplitudes from the asymptotic form and of eventual intrinsic charm in the $\eta$ and $\eta'$ mesons. We estimate the charm decay constant of the $\eta'$ meson to lie within the range $-65$ MeV $\leq f_{\eta'}^c\leq 15$ MeV.

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Online publication: August 25, 1998
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