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arXiv · hep-ph/0302200

The $η_c(3654)$ and hyperfine splitting in charmonium

A. M. Badalian·B. L. G. Bakker
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Abstract

The hyperfine splitting for the 2S charmonium state is calculated and the predicted number is $Δ_{\rm HF}(2S) = 57 \pm 8$ MeV, being by derivation the lower bound of this splitting. It results in $M(η_c(2S))= 3630 \pm 8$ MeV, which is smaller by two standard deviations than found in the Belle experiment \cite{ref.01}, but close to the $η_c(2S)$ mass observed by the same group in the experiment $e^+e^- \to J/ψη_c$ \cite{ref.06} where $M(η_c(2S)) = 3622 \pm 12$ MeV was found.

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A. M. Badalian, B. L. G. Bakker. 2003-02-21. The $η_c(3654)$ and hyperfine splitting in charmonium. https://doi.org/10.1103/physrevd.67.071901

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