${{\mathit J / \psi}{(1S)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit U}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit e}^{+}}{{\mathit e}^{-}}$  Decay Mode Summary INSPIRE   JSON  (beta) PDGID:
M070.352
Mode (*) Fraction ($\Gamma_i$ / $\Gamma$) Scale Factor/
Conf. Level		 P(MeV/c)  
$\Gamma_{374}$ ${{\mathit J / \psi}{(1S)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit U}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ $<9.11 \times 10^{-7}$ CL= 90%
Category: Dalitz decays
Note: For a dark photon ${{\mathit U}}$ with mass between 100 and 2100 MeV.
The following data is related to the above value:
$\Gamma({{\mathit J / \psi}{(1S)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit U}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit e}^{+}}{{\mathit e}^{-}})/\Gamma_{\text{total}}$
$\Gamma_{374}/\Gamma$