2,175 research outputs found
Branching ratios and CP asymmetries in charmless nonleptonic B decays to radially excited mesons
Nonleptonic two body B decays including radially excited or
mesons in the final state are studied using the framework of
generalized naive factorization approach. Branching ratios and CP asymmetries
of , , and decays are calculated, where P and V stand for pseudoscalar and
vector charmless mesons. Form factors for and transitions are estimated in the improved version of the
Isgur-Scora-Grinstein-Wise quark model. In some processes, CP asymmetries of
more than 10% and branching ratios of order are found, which could be
reached in experiments.Comment: 18 pages, 11 table
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
in an ACD model
We present a full calculation of the amplitudes for in a simple ACD model that extends an incomplete one in a previous
paper. We find cancellations between the contributions from different KK towers
and a small decrease relative to the SM predictions. It is conjectured that
radiative QCD corrections might actually lead to an enhancement in the
branching ratios and {\bf CP} asymmetries, but no more than modest ones.Comment: 3 pages, 2 figure
Precision Studies of Duality in the 't Hooft Model
We address numerical aspects of local quark-hadron duality using the example
of the exactly solvable 't Hooft model, two-dimensional QCD with N_c -->
infinity. The primary focus of these studies is total semileptonic decay widths
relevant for extracting |V_{cb}| and |V_{ub}|. We compare the exact
channel-by-channel sum of exclusive modes to the corresponding rates obtained
in the standard 1/m_Q expansion arising from the Operator Product Expansion. An
impressive agreement sets in unexpectedly early, immediately after the
threshold for the first hadronic excitation in the final state. Yet even at
higher energy release it is possible to discern the seeds of duality-violating
oscillations. We find the ``Small Velocity'' sum rules to be exceptionally well
saturated already by the first excited state. We also obtain a convincing
degree of duality in the differential distributions and in an analogue of
R_{e^+e^-}(s). Finally, we discuss possible lessons for semileptonic decays of
actual heavy quarks in QCD.Comment: 45 pages, 16 eps figures include
Non-Abelian Dipole Radiation and the Heavy Quark Expansion
Dipole radiation in QCD is derived to the second order in . A
power-like evolution of the spin-singlet heavy quark operators is obtained to
the same accuracy. In particular, relation between a
short-distance low-scale running heavy quark mass and the \barMS mass is
given. We discuss the properties of the effective QCD coupling \aw(E) which
governs the dipole radiation. This coupling is advantageous for heavy quark
physics.Comment: 12 pages, Late
Sum Rules for Heavy Flavor Transitions in the SV Limit
We show how sum rules for the weak decays of heavy flavor hadrons can be
derived as the moments of spectral distributions in the small velocity (SV)
limit. This systematic approach allows us to determine corrections to these sum
rules, to obtain new sum rules and it provides us with a transparent physical
interpretation; it also opens a new perspective on the notion of the heavy
quark mass. Applying these sum rules we derive a lower bound on the deviation
of the exclusive form factor from unity at zero recoil; likewise
we give a field-theoretical derivation of a previously formulated inequality
between the expectation value for the kinetic energy operator of the heavy
quark and for the chromomagnetic operator. We analyze how the known results on
nonperturbative corrections must be understood when one takes into account the
normalization point dependence of the low scale parameters. Relation between
the field-theoretic derivation of the sum rules and the quantum-mechanical
approach is elucidated.Comment: 72 pages, 5 figures (uuencoded ps files added using figures option),
Revised version. Paper is considerably extended to include some new results.
New section on quantum mechanical approach is adde
Heavy Quark Expansion and Preasymptotic Corrections to Decay Widths in the 't Hooft Model
We address nonperturbative power corrections to inclusive decay widths of
heavy flavor hadrons in the context of the 't Hooft model (two-dimensional QCD
at N_c->oo), with the emphasis on the spectator-dependent effects sensitive to
the flavor of the spectator. The summation of exclusive widths is performed
analytically using the `t Hooft equation. We show that the 1/m_Q expansion of
both the Weak Annihilation and Pauli Interference widths coincides with the OPE
predictions, to the computed orders. Violation of local duality in the
inclusive widths is quantified, and the new example is identified where the OPE
prediction and the actual effect are completely saturated by a single final
state. The qualitative aspects of quark hadronization emerging from the
analysis in the 't Hooft model are discussed. Certain aspects of summation of
spectator-independent hadronic weak decay widths are given in more detail,
which were not spelled out previously. We also give some useful details of the
1/m_Q expansion in the 't~Hooft model.Comment: 54 pages, 8 figures in the text. Version to be published in Phys.
Rev. D. A number of typos are corrected and relevant references added.
Clarifications in Conclusions, Appendices 2.1 and 3 are adde
On the Motion of Heavy Quarks inside Hadrons: Universal Distributions and Inclusive Decays
In previous papers we have pointed out that there exists a QCD analog of the
phenomenological concept of the so called Fermi motion for the heavy quark
inside a hadron. Here we show in a more detailed way how this comes about and
we analyze the limitations of this concept. Non-perturbative as well as
perturbative aspects are included. We emphasize both the similarities and the
differences to the well-known treatment of deep inelastic lepton-nucleon
scattering. We derive a model-independent {\em lower} bound on the kinetic
energy of the heavy quark inside the hadron.Comment: 34 pages, Latex, 4 figures. Some clarifying comments and postscript
files of figures are adde
Analytical Heavy Quark Expansion in the 't Hooft Model
We present a number of exact relations for the heavy quark limit and develop
an analytical 1/m_Q expansion for heavy mesons in the 't Hooft model. Among the
new results are relation 3\mu_\pi^2=\bar\Lambda^2 - m_{sp}^2+\beta^2, 1/m_Q
corrections to the decay constants, to the kinetic expectation values and
1/m_Q^2 nonperturbative corrections to the B->D amplitude at zero recoil. The
properties of the IW functions are addressed and the small velocity sum rules
are verified.Comment: 22 pages, plain LaTeX (no figures
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