Radiative and leptonic decays of the pseudoscalar charmonium state ${\eta }_c$

Abstract

The radiative and leptonic decays of ${\eta }_c\to \gamma \gamma$ and ${\eta }_c\to l^{+}{l}^{-}$ are studied. For ${\eta }_c\to \gamma \gamma$ decay, the second-order electromagnetic tree-level diagram gives the leading contribution. The decay rate of ${\eta }_c\to \gamma \gamma$ is calculated, the prediction is in good agreement with the experimental data. For ${\eta }_c\to l^{+}{ł}^{-}$, both the tree and loop diagrams are calculated. The analysis shows that the loop contribution dominates, the contribution of tree diagram with $Z^0$ intermediate state can only modifies the decay rate by less than 1%. The prediction of the branching ratios of ${\eta }_c\to e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$ are very tiny within the standard model. The smallness of these predictions within the standard model makes the leptonic decays of ${\eta }_c$ sensitive to physics beyond the standard model. Measurement of the leptonic decay may give information of new physics.

arXiv comment9 pages, 4 figures, RevTex, small change, version to appear in Phys. Rev. D

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• ${\chi }_{QJ}\to {\ell }^{+}{\ell }^{-}$ within and beyond the Standard Model
• Observation prospects of leptonic and Dalitz decays of pseudoscalar quarkonia
• Study on the effects of the light CP-odd Higgs via the leptonic decays of pseudoscalar mesons
• ${\eta }_c\to l^{+}{l}^{-}$ and ${\chi }_{c0}\to l^{+}{l}^{-}$ decays revisited