${\eta }^{\prime }\to \gamma \gamma$ and the topological susceptibility

Abstract

The radiative decays $η'(η)\rtaγγ$ are discussed. The modifications of the conventional PCAC formulae due to the gluonic contribution to the flavour singlet axial anomaly are given. The decay constants satisfy a modified Dashen formula which generalises the Witten--Veneziano formula for the mass of the ${\eta }^{\prime }$. It is shown how the topological susceptibility in QCD with massive, dynamical quarks may be extracted from measurements of $η'(η)\rtaγγ$.

4 pages, LaTeX, uses espcrc2.sty. To appear in Proceedings, QCD99 Montpellier

Cited by in corpus (3)

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