2,340 research outputs found
Note on Tests of the Factorization Hypothesis and the Determination of Meson Decay Constants
We discuss various tests of the factorization hypothesis making use of the
close relationship between semi-leptonic and factorized nonleptonic decay
amplitudes. It is pointed out that factorization leads to truely
model-independent predictions for the ratio of nonleptonic to semi-leptonic
decay rates, if in the nonleptonic decay a spin one meson of arbitrary mass or
a pion take the place of the lepton pair. Where the decay constants of those
mesons are known, these predictions represent ideal tests of the factorization
hypothesis. In other cases they may be used to extract the decay constants.
Currently available data on the decays are shown to be in excellent agreement with
the factorization results. A weighted average of the four independent values
for the QCD coefficient extracted from the data gives
suggesting that it may be equal to the Wilson coefficient evaluated
at the scale .Comment: (9 pages, ReVTeX, no figures), HD-THEP-92-3
\Lambda_b \to \Lambda_c P(V) Nonleptonic Weak Decays
The two-body nonleptonic weak decays of \Lambda_b \to \Lambda_c P(V) (P and V
represent pseudoscalar and vector mesons respectively) are analyzed in two
models, one is the Bethe-Salpeter (B-S) model and the other is the hadronic
wave function model. The calculations are carried out in the factorization
approach. The obtained results are compared with other model calculations.Comment: 18 pages, Late
Lattice QCD calculation of decay form factors at zero recoil
A lattice QCD calculation of the decay form factors
is presented. We obtain the value of the form factor at the
zero-recoil limit with high precision by considering a ratio of
correlation functions in which the bulk of the uncertainties cancels. The other
form factor is calculated, for small recoil momenta, from a similar
ratio. In both cases, the heavy quark mass dependence is observed through
direct calculations with several combinations of initial and final heavy quark
masses. Our results are and
. For both the first error is statistical,
the second stems from the uncertainty in adjusting the heavy quark masses, and
the last from omitted radiative corrections. Combining these results, we obtain
a precise determination of the physical combination , where the mentioned systematic errors are added in
quadrature. The dependence on lattice spacing and the effect of quenching are
not yet included, but with our method they should be a fraction of .Comment: 32 pp, 10 figs; final, published versio
in the Standard Model
In this paper we investigate the possibility of studying form
factor using the semi-inclusive decays . In general
semi-inclusive decays involve several hadronic parameters. But for
decays we find that in the factorization
approximation, the only unknown hadronic parameters are the form factors
. Therefore these form factors can be studied in decays. Using theoretical model calculations for the form
factors the branching ratios for and
, with the cut GeV, are
estimated to be in the ranges of and ,
respectively, depending on the value of . The combined branching ratio
for is about and is insensitive to . We also discuss CP
asymmetries in these decay modes.Comment: RevTex 8 pages and two figure
Non-perturbatively Improved Heavy-Light Mesons: Masses and Decay Constants
We present a study of the heavy-light spectrum and of the D- and B-meson
decay constants. The results wer e obtained in the quenched approximation, by
using the non-perturbatively improved Clover lattice action at beta=6.2, with a
sample of 100 configurations, on a 24^3 x 64 lattice. After a careful analysis
of th e systematic errors present in the extraction of the physical results, by
assuming quite conservative discretization errors, we find f_Ds=231 +/-
12^{+6}_{-1} MeV, f_D = 211 +/- 14^{+0}_{-12} MeV, f_Ds/f_D=1.10(2), f_Bs = 204
+/- 16^{+28}_{-0} MeV, f_B = 179 +/- 18^{+26}_{-9} MeV,
f_Bs/f_B=1.14(3)^{+0}_{-1}. Our results, which have smaller discretization
errors than many previous estimates at fixed value of the lattice spacing ,
support a large value of f_B in the quenched approximation.Comment: 26 pages, 9 Postscript figure
Exploring CP Violation with Decays
We point out that the pure ``tree'' decays are
particularly well suited to extract the CKM angle through amplitude
relations. In contrast to conceptually similar strategies using or decays, the advantage of the approach is that
the corresponding triangles have three sides of comparable length and do not
involve small amplitudes. Decays of the type -- the
-spin counterparts of -- can be added to the
analysis, as well as channels, where the - and -mesons are
replaced by higher resonances.Comment: 9 pages, LaTeX, 3 figures, reference adde
The CP violating phase from global fit of rare charmless hadronic B decays
We study constraints on the CP violating phase in the
Kobayashi-Maskawa model using available experimental data. We first follow the
conventional method to up date the constraint on by performing a
analysis using data from , and
. We also include the recent information on in
the analysis. We obtain the best fit for to be and the 95%
C.L. allowed range to be . We then develop a method to
carry out a analysis based on SU(3) symmetry using data from and . We also discuss SU(3) breaking effects from model
estimate. We find that present data on can also give some
constraint on although weaker than the earlier method limited by the
present experimental errors. Future improved data will provide more stringent
constraint. Finally we perform a combined fit using data from ,
, , and rare charmless
hadronic B decays. The combined analysis gives for the best
fit value and as the 95% C.L. allowed range. Several
comments on other methods to determine based on SU(3) symmetry are
also provided.Comment: Revised verion with the new experimental data from Belle and Babar
included in the analysis to obtain the global fit for the CP violating phase
gamma. RevTex, 32 pages and 8 figure
1/m_Q Corrections to the Bethe-Salpeter Equation for \Lambda_{Q} in the Diquark Picture
Corrections of order 1/m_Q (Q=b or c) to the Bethe-Salpeter (B-S) equation
for \Lambda_Q are analyzed on the assumption that the heavy baryon \Lambda_Q is
composed of a heavy quark and a scalar, light diquark. It is found that in
addition to the one B-S scalar function in the limit m_Q -> \infty, two more
scalar functions are needed at the order 1/m_Q. These can be related to the B-S
scalar function in the leading order. The six form factors for the weak
transition \Lambda_b -> \Lambda_c are expressed in terms of these wave
functions and the results are consistent with heavy quark effective theory to
order 1/m_Q. Assuming the kernel for the B-S equation in the limit m_Q ->
\infty to consist of a scalar confinement term and a one-gluon-exchange term we
obtain numerical solutions for the B-S wave functions, and hence for the
form factors to order 1/m_Q. Predictions are given
for the differential and total decay widths for \Lambda_b -> \Lambda_c l
\bar{\nu}, and also for the nonleptonic decay widths for \Lambda_b -> \Lambda_c
plus a pseudoscalar or vector meson, with QCD corrections being also included.Comment: Latex, 24 pages, two figure
Weak Decays in the light--front Quark Model
We study the form factors of heavy--to--heavy and heavy--to--light weak
decays using the light--front relativistic quark model. For the
heavy--to--heavy B \ra D^{(\ast)} semileptonic decays we calculate the
corresponding Isgur--Wise function for the whole kinematic region. For the
heavy--to--light B\ra P and B\ra V semileptonic decays we calculate the
form factors at ; in particular, we have derived the dependence of the
form factors on the --quark mass in the m_b \ra \infty limit. This
dependence can not be produced by extrapolating the scaling behavior of the
form factors at using the single--pole assumption. This shows that
the dependence of the form factors in regions far away from the
zero--recoil could be much more complicated than that predicted by the
single--pole assumption.Comment: 24 pages, Latex, Postscript figure included at the en
Combining CP Asymmetries in Decays
We prove an approximate relation, to leading order in dominant terms, between
CP-violating rate differences in and
. We show how data from these two processes may be
combined in order to enhance the significance of a nonzero result.Comment: 9 pages, latex, no figures, submitted to Phys. Rev. Letters, revise
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