A measurement of the inclusive semileptonic branching fractions and lifetime ratio of the B{sub u} and B{sub d} mesons
Separate measurements of the B{sub u} and B{sub d} semileptonic branching fractions have been made using 1.4 fb{sup {minus}1} of data taken with the CLEO-II detector at the {Upsilon}(4S) resonance. A new technique is utilized in which a {bar B} meson is exclusively reconstructed in order to tag the charge and flavor. Approximately 2000 fully reconstructed candidates are found in the data sample. Since the {Upsilon}(4S) decays to B{bar B}, the tracks from the B meson can then be examined for lepton content. The efficiency corrected ratio of the number of leptons and the number of tags determines the semileptonic branching fractions. This method allows for the first separate measurement of the charged B meson semileptonic branching ratio in contrast to other techniques which measure the flavor averaged branching fractions. Assuming that the partial semileptonic decay widths of the charged and neutral B`s are equal, the lifetime ratio can be measured from the ratio of semileptonic branching fractions. Since the flavor is explicitly tagged, no assumptions concerning the product fractions of the B{sub u} and B{sub d} (f{sub +{minus}} and f{sub 00}) are used, unlike results of past {Upsilon}(4S) experiments. Hence, with the exception of the partial semileptonic width equality, the only assumption used is that of the shape of the direct lepton (B {yields} {ell}X) momentum spectrum in efficiency determination. Theoretical dependence is thus kept at a minimum. The measured results for the branching fractions and lifetime ratio are: B(B{sup +} {yields} X{ell}{sup +}{nu}) = (13.0 {+-} 1.8 {+-} 1.6)%; B(B{sup 0} {yields} X{ell}{sup +}{nu}) = (14.5 {+-} 2.1 {+-} 1.9)%; {tau}(B{sup 0})/{tau}(B{sup +}) = 0.90 {+-} 0.18 {+-} 0.12.
- Research Organization:
- Oklahoma Univ., Norman, OK (United States)
- OSTI ID:
- 39346
- Country of Publication:
- United States
- Language:
- English
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