Search for the lepton number violating decay $\eta \to {\pi }^{+}{\pi }^{+}{e}^{-}{e}^{-}+c.c.$ via $J/\psi \to \varphi \eta$

BESIII Collaboration, M. Ablikim, M. N. Achasov +689

Based on a sample of $(10.087\pm 0.044)\times 10^{9}J/\psi$ events collected by the BESIII detector at the BEPCII collider, we perform the first search for the lepton number violati…