Using a data sample of $(1.0087 \pm 0.0044)\times10^{10}$ $J/\psi$ events collected with the BESIII detector, we study the rare double Dalitz decay $\eta\to e^+e^-e^+e^-$ through the processes $J/\psi\to\gamma\eta$ and $J/\psi\to\gamma\eta'$, with $\eta'\to\pi^+\pi^-\eta$. Clear $\eta$ signals are observed in the $e^+e^-e^+e^-$ invariant mass spectrum, with statistical significances of $5.9\sigma$ and $7.8\sigma$ for the two channels, respectively. By combining both modes, we determine the branching fraction to be $$\mathcal{B}(\eta\to e^+e^-e^+e^-) = (2.63 \pm 0.34\,(\mathrm{stat}) \pm 0.16\,(\mathrm{syst}))\times10^{-5},$$ which is consistent with previous measurements within uncertainties and provides further constraints on physics beyond the Standard Model.
Measurement of the double Dalitz decay 𝜂→𝑒+𝑒−𝑒+𝑒−
Garzia, I.;Melendi, F. M.;
2026
Abstract
Using a data sample of $(1.0087 \pm 0.0044)\times10^{10}$ $J/\psi$ events collected with the BESIII detector, we study the rare double Dalitz decay $\eta\to e^+e^-e^+e^-$ through the processes $J/\psi\to\gamma\eta$ and $J/\psi\to\gamma\eta'$, with $\eta'\to\pi^+\pi^-\eta$. Clear $\eta$ signals are observed in the $e^+e^-e^+e^-$ invariant mass spectrum, with statistical significances of $5.9\sigma$ and $7.8\sigma$ for the two channels, respectively. By combining both modes, we determine the branching fraction to be $$\mathcal{B}(\eta\to e^+e^-e^+e^-) = (2.63 \pm 0.34\,(\mathrm{stat}) \pm 0.16\,(\mathrm{syst}))\times10^{-5},$$ which is consistent with previous measurements within uncertainties and provides further constraints on physics beyond the Standard Model.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
