236 research outputs found
Charm meson resonances in decays
Motivated by recent experimental results we reconsider semileptonic decays within a model which combines heavy quark symmetry and
properties of the chiral Lagrangian. We include excited charm meson states,
some of them recently observed, in our Lagrangian and determine their impact on
the charm meson semileptonic form factors. We find that the inclusion of
excited charm meson states in the model leads to a rather good agreement with
the experimental results on the shape of the form factor. We
also calculate branching ratios for all decays.Comment: 9 pages, 4 figures; minor corrections, added some discussion, version
as publishe
Futher Study of CP Violation and Branching Ratios for and in the Standard Model and Beyond
In this work we study the CP violation for and
up to leading and next-to-leading order QCD corrections
in the standard model, two-Higgs-doublet model and the minimal supersymmetric
extension of the standard model. We also study the effect of new physics on the
branching ratios of these two decay modes. We find that within the parameter
space constrained by the observation of the decay , new physics
does not affect the CP asymmetries greatly, and the prediction of new physics
to the branching ratios of and is the same as that of the standard model up to a minor discrepancy as far
as the Yukama couplying constants are perturbative.Comment: some figures being reduced, accepted by J. Physics
Final-state interaction and s-quark helicity conservation in B -> J/psi K*
The Section of charm quark spin conservation is deleted since it involves
more dynamical assumptions than previously stated. A few comments are added in
view of new experimental results.Comment: To replace the earlier version of hep-ph/0106354. Minor additions and
one deletion with no change in the main argument nor the conclusio
Determination of the CP Violating Phase by a Sum Over Common Decay Modes to and
To help the difficult determination of the angle of the unitarity
triangle, Aleksan, Dunietz and Kayser have proposed the modes of the type
, common to and . We point out that it is possible
to gain in statistics by a sum over all modes with ground state mesons in the
final state, i.e. , , , .
The delicate point is the relative phase of these different contributions to
the dilution factor of the time-dependent asymmetry. Each contribution to
is proportional to a product where
denotes form factors and decay constants. Within a definite phase
convention, lattice calculations do not show any change in sign when
extrapolating to light quarks the form factors and decay constants. Then, we
can show that all modes contribute constructively to the dilution factor,
except the -wave , which is small. Quark model arguments
based on wave function overlaps also confirm this stability in sign. By summing
over all these modes we find a gain of a factor 6 in statistics relatively to
. The dilution factor for the sum is remarkably stable for
theoretical schemes that are not in very strong conflict with data on or extrapolated from semileptonic charm form factors, giving
, always close to .Comment: 22 pages, LPTHE Orsay 94/03, DAPNIA/SPP/94-2
Decay
Motivated by the experimental measurement of the decay rate, , and
the longitudinal polarization, , in the Cabibbo favored decay , we have studied theoretical prediction within the context of
factorization approximation invoking several form factors models. We were able
to obtain agreement with experiment for both and by using
experimentally measured values of the form factors ,
and in the semi-leptonic decay . We have also included in our calculation the effect of the
final state interaction () by working with the partial waves amplitudes
, and . Numerical calculation shows that the decay amplitude is
dominated by wave, and that the polarization is sensitive to the
interference between and waves. The range of the phase difference
accommodated by experimental error in
is large.Comment: 7 pages, LaTe
The semileptonic B->pi decay in a Constituent Quark-Meson model
We evaluate the form factors describing the exclusive decay B-> pi l nu by
using a Constituent Quark-Meson model based on an effective quark-meson
Lagrangian (CQM). The model allows for an expansion in the pion momenta and we
consider terms up to the first order in the pion field derivatives. We compute
the leading terms in the soft pion limit and consider corrections to this
limit.Comment: 6 pages, 3 figures, LaTeX (uses aps, epsf, revtex), formula 26
corrected, discussion enlarged, references updated and other minor change
Uncertainties on the CP Phase \bfalpha due to Penguin Diagrams
A major problem in the determination of the the CP angle , that
should be measured through modes of the type is the uncertainty coming from Penguin diagrams. We consider the
different ground state modes , , , and, assuming
the FSI phases to be negligible, we investigate the amount of uncertainty
coming from Penguins that can be parametrized by a dilution factor and an
angle shift . The parameter is either 1 or very close to 1
in all these modes, and it can be measured independently, up to a sign
ambiguity, by the dependence. Assuming factorization, we show that is much smaller for the modes and than for , and we plot their allowed region as a function of itself.
Moreover, we show that most of the modes contribute to the asymmetry with the
same sign, and define for their sum an effective and an effective
, an average of for the different modes.
It turns out that is of the order of 0.9, is
between 5 and 10 and, relative to , the statistical gain for
the sum is of about a factor 10. Finally, we compute the ratios that test the strength of the Penguins and depend on the CP angles,
as emphasized by Silva and Wolfenstein and by Deandrea et al.Comment: 18 page
Nonfactorization and Color-Suppressed Decays
Using value of the parameter but including a modest
nonfactorized amplitude, we show that it is possible to understand all data,
including polarization, for color-suppressed
decays in all commonly used models of form factors. We show that for decay one can define an effective , which is process-dependent and,
in general, complex; but it is not possible to define an effective for
decay. We also explain why nonfactorized amplitudes do not
play a significant role in color-favored B decays.Comment: 13 pages, Latex, one figure (not included
Can there be any new physics in b -> d penguins
We analyze the possibility of observing new physics effects in the
penguin amplitudes. For this purpose, we consider the decay mode , which has only penguin contributions. Using the QCD
factorization approach, we find very tiny CP violating effects in the standard
model for this process. Furthermore, we show that the minimal supersymmetric
standard model with mass insertion and R-parity violating supersymmetric
model can provide substantial CP violation effects. Observation of sizable CP
violation in this mode would be a clear signal of new physics.Comment: Published versio
Consistent Analysis of the Transition Form Factor in the Whole Physical Region
In the paper, we show that the transition form factor can be
calculated by using the different approach in the different regions and
they are consistent with each other in the whole physical region. For the
transition form factor in the large recoil regions, one can apply the
PQCD approach, where the transverse momentum dependence for both the hard
scattering part and the non-perturbative wavefunction, the Sudakov effects and
the threshold effects are included to regulate the endpoint singularity and to
derive a more reliable PQCD result. Pionic twist-3 contributions are carefully
studied with a better endpoint behavior wavefunction for and we find
that its contribution is less than the leading twist contribution. Both the two
wavefunctions and of the B meson can give sizable
contributions to the transition form factor and should be kept for a
better understanding of the B decays. The present obtained PQCD results can
match with both the QCD light-cone sum rule results and the extrapolated
lattice QCD results in the large recoil regions.Comment: 18pages, 6 figure
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