Search for the double-charmonium state with ηcJ/ψ at Belle

jats:titleAjats:scbstract</jats:sc> </jats:title>jats:pWe measure the cross section of jats:italice</jats:italic>jats:sup+</jats:sup>jats:italice</jats:italic>jats:supjats:italic−</jats:italic></jats:sup> → jats:italicη</jats:italic>jats:subjats:italicc</jats:italic></jats:sub>jats:italicJ/ψ</jats:italic> at the Υ(jats:italicnS</jats:italic>)(jats:italicn</jats:italic> = 1–5) on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector with an integrated luminosity of 955 fbjats:supjats:italic−</jats:italic>1</jats:sup>. We also search for double charmonium production in jats:italice</jats:italic>jats:sup+</jats:sup>jats:italice</jats:italic>jats:supjats:italic−</jats:italic></jats:sup> → jats:italicη</jats:italic>jats:subjats:italicc</jats:italic></jats:sub>jats:italicJ/ψ</jats:italic> via initial state radiation near the jats:italicη</jats:italic>jats:subjats:italicc</jats:italic></jats:sub>jats:italicJ/ψ</jats:italic> threshold. No evident signal of the double charmonium state is found, but evidence for the jats:italice</jats:italic>jats:sup+</jats:sup>jats:italice</jats:italic>jats:supjats:italic−</jats:italic></jats:sup>jats:italic→ η</jats:italic>jats:subjats:italicc</jats:italic></jats:sub>jats:italicJ/ψ</jats:italic> process is found with a statistical significance greater than 3jats:italic.</jats:italic>3jats:italicσ</jats:italic> near the jats:italicη</jats:italic>jats:subjats:italicc</jats:italic></jats:sub>jats:italicJ/ψ</jats:italic> threshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.</jats:p>