An overlooked WZW structure in the HLS formulation of vector mesons produces topological quantization of their anomalous couplings.
Observation of the Dalitz Decay $\eta' \to \gamma e^+e^-$
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abstract
We report the first observation of the Dalitz decay $\eta' \to \gamma e^+e^-$, based on a data sample of 1.31 billion $J/\psi$ events collected with the BESIII detector. The $\eta'$ mesons are produced via the $J/\psi \to \gamma \eta'$ decay process. The ratio $\Gamma(\eta' \to \gamma e^+ e^-)/\Gamma(\eta'\to\gamma\gamma)$ is measured to be $(2.13\pm0.09(\text{stat.})\pm0.07(\text{sys.}))\times10^{-2}$. This corresponds to a branching fraction ${\cal B}(\eta' \to \gamma e^+e^-)= (4.69 \pm0.20(\text{stat.})\pm0.23(\text{sys.}))\times10^{-4}$. The transition form factor is extracted and different expressions are compared to the measured dependence on the $e^+e^-$ invariant mass. The results are consistent with the prediction of the Vector Meson Dominance model.
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hep-ph 2representative citing papers
The Standard Model value for the muon anomalous magnetic moment is 116591810(43)×10^{-11}, 3.7σ below the Brookhaven experimental measurement.
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Topological quantization of vector meson anomalous couplings
An overlooked WZW structure in the HLS formulation of vector mesons produces topological quantization of their anomalous couplings.
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The anomalous magnetic moment of the muon in the Standard Model
The Standard Model value for the muon anomalous magnetic moment is 116591810(43)×10^{-11}, 3.7σ below the Brookhaven experimental measurement.