Production of B_c Mesons in Photon-Photon and Hadron-Hadron Collisions

We discuss two-photon and hadronic production of $B_c$ mesons in nonrelativistic bound state approximation and to lowest order in the coupling constants $\alpha$ and $\alpha_s$. It is shown that in photon-photon collisions, heavy quark fragmentation is dominated by recombination of $\bar b$ and $c$ quarks up to the highest accessible transverse momenta. In contrast, in hadroproduction, which at high energies mainly involves gluon--gluon collisions, the fragmentation mechanism dominates at transverse momenta $p_T > m_{B_c}$, providing a simple and satisfactory approximation of the complete $O(\alpha_s^4)$ results in the high-$p_T$ regime. Contradictions in previous publications on hadroproduction of $B_c$ mesons are clarified. We also present predictions for cross sections and differential distributions at present and future accelerators.