A new $G$-parity violating amplitude in the $J/\psi$ decay?

Abstract

The $J/\psi$ meson has negative $G$-parity so that, in the limit of isospin conservation, its decay into ${\pi }^{+}{\pi }^{-}$ should be purely electromagnetic. However, the measured branching fraction $\mathcal{B}(J/\psi \to {\pi }^{+}{\pi }^{-})$ exceeds by more than 3.9 standard deviations the expectation computed according to BaBar data on the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ cross section. The possibility that the two-gluon plus one-photon decay mechanism is not suppressed by $G$-parity conservation is discussed, even by considering other multi-pion decay channels. As also obtained by phenomenological computation, such a decay mechanism could be responsible for the observed discrepancy. Finally, we notice that the BESIII experiment, having the potential to perform an accurate measurement of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ cross section in the 3 GeV energy region, can definitely prove or disprove this strong $G$-parity-violating mechanism by confirming or confuting the BaBar data.

arXiv comment12 pages, 7 figures

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Cited by in corpus (1)

• $G$-parity violating amplitudes in the $J/\psi \to {\pi }^{+}{\pi }^{-}$ decay