Search for the double-charmonium state with ${\eta }_{c}J/\psi$ at Belle

Belle Collaboration, J. H. Yin, Y. B. Li +180

We measure the cross section of $e^{+}{e}^{-}\to {\eta }_{c}J/\psi$ at the ${\rm Y}(nS)(n=1$ -- $5)$ on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected b…