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η′(η) → γγ : A Tale of Two Anomalies / G. M. Shore, Graham Shore

Phys. Scripta, Volume: T99, Pages: 84 - 95

Swansea University Author: Graham Shore

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DOI (Published version): 10.1238/Physica.Topical.099a00084

Abstract

The radiative decays of the pseudoscalar mesons P = (π0,η,η′) are of special interest as they provide an experimental window on the electromagnetic and colour chiral UA(1) anomalies. π0 → γγ is well described by the electromagnetic UA(1) anomaly under the assumption that π0 is a Goldstone boson for...

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Published in: Phys. Scripta
Published: 2002
URI: https://cronfa.swan.ac.uk/Record/cronfa17512
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Abstract: The radiative decays of the pseudoscalar mesons P = (π0,η,η′) are of special interest as they provide an experimental window on the electromagnetic and colour chiral UA(1) anomalies. π0 → γγ is well described by the electromagnetic UA(1) anomaly under the assumption that π0 is a Goldstone boson for spontaneously broken chiral symmetry, but the analogous results for η′(η) → γγ are complicated by the colour UA(1) anomaly in QCD. This paper reviews the theory of η′(η) → γγ decays, emphasising the role of the colour UA(1) anomaly and the renormalisation group. The relation to the Witten-Veneziano mass formula for the η′ and the QCD topological susceptibility is derived. The implications for the phenomenological analysis of P → γγ are described and a proposal is made for a comprehensive re-analysis of existing data on P → γγ, P → V γ, where V = (ρ, ω, φ) is a light 1− meson, η′(η) → ππγ, ψ → η′(η)γ, etc. Other applications, to the muon anomalous magnetic moment gμ − 2 and the determination of the photon structure function g1γ in polarised deep inelastic scattering, are also briefly discussed.
College: College of Science
Start Page: 84
End Page: 95