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Radiative and leptonic decays of the pseudoscalar charmonium state ηc\eta_c

Abstract

The radiative and leptonic decays of ηcγγ\eta_c\to \gamma\gamma and ηcl+l\eta_c\to l^+l^- are studied. For ηcγγ\eta_c\to \gamma\gamma decay, the second-order electromagnetic tree-level diagram gives the leading contribution. The decay rate of ηcγγ\eta_c\to \gamma\gamma is calculated, the prediction is in good agreement with the experimental data. For \eta_c\to l^+\l^-, both the tree and loop diagrams are calculated. The analysis shows that the loop contribution dominates, the contribution of tree diagram with Z0Z^0 intermediate state can only modifies the decay rate by less than 1%. The prediction of the branching ratios of ηce+e\eta_c\to e^+e^- and μ+μ\mu^+\mu^- are very tiny within the standard model. The smallness of these predictions within the standard model makes the leptonic decays of ηc\eta_c sensitive to physics beyond the standard model. Measurement of the leptonic decay may give information of new physics.Comment: 9 pages, 4 figures, RevTex, small change, version to appear in Phys. Rev.

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    Last time updated on 02/01/2020