Production of doubly heavy-flavored hadrons at $e^+e^-$ colliders

Production of the doubly heavy-flavored hadrons ($B_c$ meson, doubly heavy baryons $\Xi_{cc}$, $\Xi_{bc}$, $\Xi_{bb}$, their excited states and antiparticles of them as well) at $e^+e^-$ colliders is investigated under two different approaches: $LO$ (leading order QCD complete calculation) and $LL$ (leading logarithm fragmentation calculation). The results for the production obtained by the approaches $LO$ and $LL$, including the angle distributions of the produced hadrons with unpolarized and polarized incoming beams, the behaviors on the energy fraction of the produced doubly heavy hadron and comparisons between the two approaches' results, are presented in terms of tables and figures. Thus characteristics of the production and uncertainties of the approaches are shown precisely, and it is concluded that only if the colliders run at the eneries around $Z$-pole (which may be called as $Z$-factories) and additionally the luminosity of the colliders is as high as possible then to study the doubly heavy hadrons thoroughly is accessible.