Key Distributions for Charmless Semileptonic B Decay

We present theoretical predictions for a few phenomenologically interesting distributions in the semileptonic b->u decays which are affected by Fermi motion. The perturbative effects are incorporated at the one-loop level and appear to be very moderate. Our treatment of Fermi motion is based directly on QCD, being encoded in the universal distribution function F(x). The decay distributions in the charged lepton energy, invariant mass of hadrons, hadron energy, and q^2 are given. We note that typically about 90% of all decay events are expected to have M_X < M_D; this feature can be exploited in determination of |V_ub|.Comment: 9 pages, 6 figures (incorporated in the LaTeX file); plain LaTe

Strong interaction effects in semileptonic B decays

Strong interaction effects are addressed in connection to extracting |V_{cb}|. A comprehensive approach is described not relying on a 1/m_c expansion; it allows a percent accuracy without ad hoc assumptions about higher-order effects. An alternative to the M_X^2 variable is proposed improving convergence. Intrinsic hardness of integrated observables with a cut on E_\ell is discussed; it can be responsible for the behavior of reported by BaBar. Consequences of the proximity to the `BPS' limit are considered.Comment: 5 pages (two-column), LaTeX, uses espcrc2.sty. Talk given at ICHEP-2002, July 24-31 2002, Amsterda

Nonperturbative Corrections to Inclusive Beauty and Charm Decays: QCD versus Phenomenological Models

We present a selfconsistent method for treating nonperturbative effects in inclusive nonleptonic and semileptonic decays of heavy flavour hadrons. These effects give rise to powerlike corrections $\propto 1/m_Q^n\,$, $n \ge 2$ with $m_Q$ denoting the heavy quark mass.The leading correction to the semileptonic branching ratio occurs for n=2. It is expressed in terms of the vector-pseudoscalar mass splitting: \delta BR\ind{sl}/BR\ind{sl} \simeq BR\ind{nl}\, \cdot \,6\,(\,(M_V^2-M_P^2)/m_Q^2)\cdot (c_+^2 - c_-^2)/2N_c and yields a {\it reduction} of BR\ind{sl}. This nonperturbative correction contributes to the nonleptonic width with a sign opposite to that of the perturbative terms that are non-leading in $1/N_c$. In beauty decays the former reduces the latter by 20 \% whereas in charm decays they more or less cancel. This leads to a {\it reduction} of BR\ind{sl} by no more than 10 \% in beauty decays and by a factor of roughly two in charm decays. We confront these results with those obtained from phenomenological models of heavy flavour decays and find that such models are unable to mimic these leading corrections by a specific choice of quark masses or by invoking Fermi motion.Comment: 11 pages (2 figs are not included), Latex file, FERMILAB-PUB-92/158-T UND-HEP-92-BIG04 TPI-MINN-92/30-

Moments of semileptonic B decay distributions in the 1/m_b expansion

We report the OPE-based predictions for a number of lepton energy and hadronic mass moments in the inclusive semileptonic B -> X_c \ell\nu decays with a lower cut on the charged lepton energy. We rely on the direct OPE approach where no expansion in the charm mass is employed and the theoretical input is a limited set of underlying OPE parameters including m_b and m_c. A Wilsonian treatment with a `hard' cutoff is applied using running low-scale masses m_Q(\mu) and kinetic expectation value \mu_\pi^2(\mu). This leaves for perturbative corrections only genuinely short-distance effects and makes them numerically small. Predictions are also given for the modified hadronic moments of the kinematic variable \cal N_X^2 which is a combination of M_X^2 and E_X. Measurement of such moments would allow a more reliable extraction of higher-order nonperturbative heavy quark parameters from experiment.Comment: 16 pages, LaTeX, three figure

Shape Variables for the Doubly-Charmed B Decays

We propose to use the hadronic shape variables to test the assumption of ``local duality'' in the doubly-charmed B decays, $B\rightarrow X_{c\bar c s}$. We compute these shape variables at leading order in parton model, and discuss how they can be compared with the experimental values.Comment: 8 pages, uses phyzzx.tex and epsf.tex, 2 figures include

Inclusive BcB_c Decays As A QCD Lab

Phenomenological models of heavy flavour decays differ significantly in their predictions of global features of $B_c$ decays, like the $B_c$ lifetime or the relative weight of c\ra s and b\ra c transitions. The $1/m_Q$ expansion which is directly based on QCD allows predictions on the pattern to be expected, namely $\tau (B_c)$ to lie well below 1 psec with c\ra s dominating over b\ra c and a reduced semileptonic branching ratio. Due to interference effects one also predicts a lower charm content in the final states of $B_c$ decays than naively anticipated. The numerical aspect of the predictions, however, has to be viewed with considerable caution since one cannot expect the $1/m_c$ expansion to converge readily for $\Delta C=1$ transitions.Comment: 9 pages; LATEX, no figures; submitted for publicatio

On the Determination of ∣Vub∣|V_{ub}| from Inclusive Semileptonic Decay Spectra

We propose a model independent method to determine $|V_{ub}|$ from the energy spectrum of the charged lepton in inclusive semileptonic $B$ decays. The method includes perturbative QCD corrections as well as nonperturbative ones.Comment: LaTeX, 19 pages, 8 figures appended after \end{document} as uu-encoded and compressed .eps files, uses epsf, Technion-PH-94/9, CERN-TH.7308/9

Theoretical Aspects of the Heavy Quark Expansion

I give a brief outline of the theoretical framework for the modern treatment of the strong interaction effects in heavy quark decays, based on first principles of QCD. This model-independent approach is required to meet the precision of current and future experiments. Applications to a few problems of particular practical interest are reviewed, including the precise determination of V_{cb} and V_{ub}. I emphasize the peculiarities of simultaneously accounting for the perturbative and power-suppressed effects necessary for accurate predictions.Comment: 18 pages, 2 Figures in the text; LaTeX. Invited lecture presented at the Workshop "Beauty `96", Rome, 17-21 June 1996; Minor stylistic changes, typos corrected, a double reference deleted; to appear in Proc. "Beauty `96" (Nucl. Instrum. & Methods A, 1996

The Baffling Semileptonic Branching Ratio of BB Mesons

The apparent gap between the measured and the expected value for the semileptonic branching ratio of $B$ mesons has become more serious over the last year. This is due to the improved quality of the data and to the increasing maturity of the theoretical treatment of non-perturbative corrections. We discuss various theoretical options to reduce the semileptonic $B$ branching ratio; among the more spectacular resolutions of the apparent puzzle is the possibility of an unorthodox enhancement in non-perturbative corrections or even of an intervention by `New Physics'. Phenomenological implications of such scenarios are pointed out.Comment: 16 Latex pages; 4 figures to be obtained from I.Bigi; preprint CERN-TH.7082/93; some misprints in the original version have been corrected and some references adde

Theoretical Update of the Semileptonic Branching Ratio of B Mesons

We reconsider the prediction of the semileptonic branching ratio of B mesons, using a recent calculation of the radiative corrections with account for finite quark masses in nonleptonic decays and taking into account 1/m_b^2 corrections. For the semileptonic branching ratio we obtain B_SL =(11.8\pm 1.6)% using pole quark masses and B_SL = (11.0\pm 1.9)% using running MS-bar quark masses. The uncertainty is dominated by unknown higher order perturbative corrections. We conclude that the present accuracy of the theoretical analysis does not allow to state a significant disagreement with the experimental results. However, our re-analysis of the decay b->ccs yields an increase of (35\pm 11)% due to next-to-leading order corrections including mass dependent terms, which further emphasizes the problem of the average charm quark content of the final states in B decays. Abstract of the erratum: Some of the numerical results presented in our paper PLB 342 (1995) 362 are affected by an error in the computer program and need to be revised. The numerical changes are, however, marginal. We take the opportunity to incorporate the complete results for the quark mass dependence of the radiative corrections to the subprocess b->ccs and enlarge the discussion of the average charm quark content in the final state, giving the results in two different renormalization schemes and adding a figure with charm quark content plotted vs. the semileptonic branching ratio.Comment: 14 pages latex plus one PS figure, uses epsf.sty and a4wide.sty; Erratum to published version appende