B _c and$b\bar bc\bar c$ at theZ ⁰-boson pole

Abstract

The cross-section for the production of$b\bar bc\bar c$ quarks ine ⁺ e ⁻ annihilation, that proves to be at a level of$\sigma (e^ + e^ - \to b\bar bc\bar c)/\sigma (e^ + e^ - \to b\bar b) \sim 10^{ - 2}$ for$\sqrt s = M_Z$ is calculated within the frames of the QCD perturbation theory. The cross sections for the associated production of 1S-and 2S-wave states ofB _c-meson in the reaction$e^ + e^ - \to B_c b\bar c$ were calculated in the nonrelativistic model of a heavy quarkonium. The number ofΛ _bc -hyperons to be expected at LEP is estimated on the basis of the assumption on quark-hadron duality.