Relativistic corrections to double $B_c$ meson production in $e^{+}{e}^{-}$ annihilation

Within the framework of nonrelativistic QCD (NRQCD) factorization, we investigate the relativistic corrections to the production of double $B_c$ mesons in $e^{+}{e}^{-}$ annihilation. The study covers center-of-mass energies from the production threshold up to $2m_Z$, considering both the photon and $Z^0$-boson propagated processes. We find that the relativistic corrections are significant, with the corresponding $K$ factors of approximately 0.6. The azimuthal asymmetry, angular distribution, and transverse momentum distribution are also presented.