209 research outputs found
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 , with
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 . 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, .
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 Decays As A QCD Lab
Phenomenological models of heavy flavour decays differ significantly in their
predictions of global features of decays, like the lifetime or the
relative weight of c\ra s and b\ra c transitions. The expansion
which is directly based on QCD allows predictions on the pattern to be
expected, namely 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
decays than naively anticipated. The numerical aspect of the predictions,
however, has to be viewed with considerable caution since one cannot expect the
expansion to converge readily for transitions.Comment: 9 pages; LATEX, no figures; submitted for publicatio
On the Determination of from Inclusive Semileptonic Decay Spectra
We propose a model independent method to determine from the energy
spectrum of the charged lepton in inclusive semileptonic 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 Mesons
The apparent gap between the measured and the expected value for the
semileptonic branching ratio of 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
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
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