20 research outputs found
B decay shape variables and the precision determination of |Vcb| and mb
We present expressions for shape variables of B decay distributions in
several different mass schemes, to order and
(Lambda_{QCD}/mb)^3. Such observables are sensitive to the b quark mass and
matrix elements in the heavy quark effective theory, and recent measurements
allow precision determinations of some of these parameters. We perform a
combined fit to recent experimental results from CLEO, BABAR, and DELPHI, and
discuss the theoretical uncertainties due to nonperturbative and perturbative
effects. We discuss the possible discrepancy between the OPE prediction, recent
BABAR results and the measured branching fraction to D and D* states. We find
|Vcb| = (40.8 +- 0.9) x 10^{-3} and mb^{1S} = 4.74 +- 0.10 GeV, where the
errors are dominated by experimental uncertainties.Comment: 23 pages, 3 figures, Version to appear in PR
Nonresonant Semileptonic Heavy Quark Decay
In both the large N_c limit and the valence quark model, semileptonic decays
are dominated by resonant final states. Using Bjorken's sum rule in an
"unquenched" version of the quark model, I demonstrate that in the heavy quark
limit nonresonant final states should also be produced at a significant rate.
By calculating the individual strengths of a large number of exclusive two-body
nonresonant channels, I show that the total rate for such processes is highly
fragmented. I also describe some very substantial duality-violating suppression
factors which reduce the inclusive nonresonant rate to a few percent of the
total semileptonic rate for the finite quark masses of B decay, and comment on
the importance of nonresonant decays as testing grounds for very basic ideas on
the structure, strength, and significance of the quark-antiquark sea and on
quark-hadron duality in QCD.Comment: 51 pages, 2 Postscript figure