Study of the semileptonic decays of B mesons into electrons

A search for electrons in e+e- annihilations at the Upsilon(4S) resonance using the CLEO detector at the Cornell Electron Storage Ring (CESR) has been conducted. An enhancement in the inclusive electron cross section which is interpreted as due to the semileptonic decays of B mesons has been observed. These mesons carry a new bare hadronic flavor, called bottom or beauty. The branching fraction for the semileptonic decay of the B meson into electrons has been measured as 12.7 +/- 2.1 +/- 1.3%, and agrees well with the predictions of a spectator quark model. The measured step in R above the Upsilon(4S) resonance is 0.53 +/- 0.22, consistent with the continuum production of B mesons containing a quark with charge 1/3. The electron events from the semileptonic decay of B mesons have been used to determine certain properties of the weak decays of the b-quark. In particular, the branching ratio for the decay B → tau anti nu/sub tau/ is less than 40.0% at the 90% Confidence Level (C.L.). This limit implies that the b-quark could decay to a u-quark some of the time, but the momentum spectrum of the electrons indicates most decays are of the b → c type. This result is substantiated by the measurement of the number of kaons per B meson semileptonic decay of 0.6 +/- 0.8. Furthermore, an upper limit on the rate of flavor changing neutral currents has been obtained. The ratio of dielectron events to single electron events is less than 0.18 at the 90% C.L. This limit implies that the b-quark decays mostly by charged currents. Finally, the ratio of like-sign dielectron events to unlike-sign dielectron events sets a limit for the probability of B0 → anti B0 transitions to less than 50%