Direct $CP$ Violation in a Variety of $B$ Decays

Abstract

We give a brief review of direct $CP$ violation effects in charmless $B$ decays, both at the inclusive and at the exclusive level. It is emphasized that typical exclusive final states are composed of 2--4 $K$ or $π$'s, hence particle identification (in terms of $K/π$ separation) is of crucial importance for studying $CP$ violation in these modes. Another kind of ``charmless" final state is also emphasized: $b\to dc\bar c$. The decay rate is tree dominant, while ``$q^2$" is necessarily above $c\bar c$ threshold hence in the domain of perturbative QCD. The $CP$ asymmetry is therefore relatively clean and reliable. Theoretically, a few $\times 10^7$ $B$'s would suffice if one could accumulate modes like $B^+\to D^{+\left(*\right)} \bar D^{0\left(*\right)}$. [To appear in proceedings of ``The Third KEK Topical Conference on CP Violation --- Its Implications to Particle Physics and Cosmology'', 16--18 November, 1993, KEK, Tsukuba, Japan (Eds. Y. Kuno and Y. Okada).]