Study of the electromagnetic Dalitz decay $J/\psi \to e^{+}{e}^{-}{\pi }^0$

Abstract

We report the first measurement of the di-electron invariant mass dependent transition form factor in the electromagnetic Dalitz decay $J/\psi \to e^{+}{e}^{-}{\pi }^0$ using $(10087\pm 44)\times 10^6$ $J/\psi$ events collected by the BESIII detector. A clear $\rho -\omega$ interference structure is observed, consistent with the pion form factor, which offers a novel approach to extract the hadronic vacuum polarization contribution to the anomalous muon magnetic moment ($a_{\mu }$) and refine the predictions of the Vector Meson Dominance (VMD) model and hadronic light-by-light contribution to $a_{\mu }$. By taking into account the contribution of this $\rho -\omega$ interference structure, the branching fraction of $J/\psi \to e^{+}{e}^{-}{\pi }^0$ in the full $e^{+}{e}^{-}$ invariant mass range is also measured for the first time to be $(8.06\pm 0.31(\mathrm{stat})\pm 0.38(\mathrm{syst}))\times 10^{-7}$, approximately twice the non-resonant VMD prediction.

arXiv comment9 pages, 4 figures

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Cited by in corpus (1)

• Dispersive analysis of the $J/\psi \to {\pi }^0{\gamma }^{\ast }$ transition form factor with $\rho$-$\omega$ mixing effects