Leptonic and semileptonic decays of charm and bottom hadrons

The authors review the experimental measurements and theoretical descriptions of leptonic and semileptonic decays of particles containing a single heavy quark, either charm or bottom. Measurements of bottom semileptonic decays are used to determine the magnitudes of two fundamental parameters of the standard model, the Cabibbo-Kobayashi-Maskawa matrix elements {ital V}{sub {ital cb}} and {ital V}{sub {ital ub}}. These parameters are connected with the physics of quark flavor and mass, and they have important implications for the breakdown of {ital CP} symmetry. To extract precise values of {parallel}{ital V}{sub {ital cb}}{parallel} and {parallel}{ital V}{sub {ital ub}}{parallel} from measurements, however, requires a good understanding of the decay dynamics. Measurements of both charm and bottom decay distributions provide information on the interactions governing these processes. The underlying weak transition in each case is relatively simple, but the strong interactions that bind the quarks into hadrons introduce complications. The authors also discuss new theoretical approaches, especially heavy-quark effective theory and lattice QCD, which are providing insights and predictions now being tested by experiment. An international effort at many laboratories will rapidly advance knowledge of this area of physics during the next decade.