B meson decays: b → c

There has recently been substantial progress in understanding b → c decays, the dominant decays of B mesons. New measurements of the antiB0 and B- masses show that the isospin mass splitting is much smaller than was suggested by previous measurements. A number of new exclusive hadronic decay modes have been detected, including three involving a Ds- and another charmed meson. Still, the branching ratios of the observed exclusive hadronic modes total only about 9%. New measurements of inclusive and exclusive semileptonic b → c decays yield central values for the CKM matrix element for b → c transitions in the range 0.035 ≤ |Vcb| ≤ 0.046. Measurements in the B sector are now sufficiently precise that systematic errors due to theoretical uncertainties and errors in the branching ratios of hadronic D decays are significant. The most surprising result is the observation of Υ (4S) → J/ψX events in which the momentum of the J/ψ is above the kinematic limit for J/ψ from B decay. This is the first evidence for Υ (4S) decays to anything other than BantiB; at present there is no compelling theoretical explanation for these events. (author) 66 refs.; 17 figs.; 11 tabs