New puzzle in charmonium decays

Abstract

By analyzing existing data on pseudoscalar charmonium decays, we obtain the ratio of the branching fractions of ${\eta }_c(2S)$ and ${\eta }_c$ decays into ten different final states with light hadrons. For the first time, we test the two existing theoretical predictions of these decays, and find that the experimental data are significantly different from both of them. The lack of observation of any decay mode with higher rate in ${\eta }_c(2S)$ than in ${\eta }_c$ decays suggests very unusual decay dynamics in pseudoscalar charmonium decays to be identified. We also report the first model-independent evaluation of the partial width of ${\eta }_c(2S)\to \gamma \gamma$ ($2.21_{-0.64}^{+0.88}$ keV) and improved determination of that of ${\eta }_c\to \gamma \gamma$ ($5.43_{-0.38}^{+0.41}$ keV). The latter shows a tension with the most recent lattice QCD calculation.

arXiv comment10 pages

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Cited by in corpus (5)

• Precise determination of decay rates for ${\eta }_c\to \gamma \gamma$, $J/\psi \to \gamma {\eta }_c$ and $J/\psi \to {\eta }_c{e}^{+}{e}^{-}$ from lattice QCD
• First-principle calculation of ${\eta }_c\to 2\gamma$ decay width from lattice QCD
• Updated measurements of the M1 transition $\psi (3686)\to \gamma {\eta }_c(2S)$ with ${\eta }_c(2S)\to K\bar{K}\pi$
• Evidence for ${\eta }_c$(2S)$\to\pipieta$ decay
• Radiative Decays of Vector Mesons with Light-Cone Sum Rules