Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
1996-03-02
Nucl.Phys.B483:339-370,1997
Physics
High Energy Physics
High Energy Physics - Phenomenology
32 pages, 5 postscript figures included, revised version to appear in Nuclear Physics B
Scientific paper
10.1016/S0550-3213(96)00559-7
We present a model-independent study of spectator effects, which are responsible for the lifetime differences between beauty hadrons. These effects can be parametrized in terms of hadronic matrix elements of four four-quark operators. For $B$ mesons, the coefficients of the non-factorizable operators turn out to be much larger than those of the factorizable ones, limiting considerably the usefulness of the vacuum insertion approximation. Non-factorizable contributions to the lifetime ratio $\tau(B^-)/\tau(B_d)$ could naturally be of order 10--20%, and not even the sign of these contributions can be predicted at present. In the case of the $\Lambda_b$ baryon, heavy-quark symmetry is used to reduce the number of independent matrix elements from four to two. In order to explain the large deviation from unity in the experimental result for $\tau(\Lambda_b)/\tau(B_d)$, it is necessary that these baryon matrix elements be much larger than those estimated in quark models. We have also reexamined the theoretical predictions for the semileptonic branching ratio of $B$ mesons and charm counting, finding that, given the present theoretical and experimental uncertainties, there is no significant discrepancy with experiment.
Neubert Matthias
Sachrajda Chris T.
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