829 research outputs found
Comments on the Quark Content of the Scalar Meson
Based on the measurements of we determine, in
a model independent way, the allowed content in the scalar meson
. We find that, on the one hand, if this isoscalar resonance is a
pure state [ , a very
large -annihilation term will be needed to accommodate . On the other hand, the component of
should be small enough to avoid excessive induced
from the external -emission. Measurement of production in the
decay will be useful to test the above picture. For the
decay which is kinematically barely or even not
allowed, depending on the mass of , we find that the finite width
effect of plays a crucial role on the resonant three-body decay
.Comment: 12 pages, 2 figure
Hadronic Charmed Meson Decays Involving Tensor Mesons
Charmed meson decays into a pseudoscalar meson P and a tensor meson T are
studied. The charm to tensor meson transition form factors are evaluated in the
Isgur-Scora-Grinstein-Wise (ISGW) quark model. It is shown that the
Cabibbo-allowed decay is dominated by the
W-annihilation contribution and has the largest branching ratio in
decays. We argue that the Cabibbo-suppressed mode
should be suppressed by one order of magnitude relative to . When the finite width effect of the tensor resonances is taken
into account, the decay rate of is generally enhanced by a factor of
. Except for , the predicted branching ratios
of decays are in general too small by one to two orders of magnitude
compared to experiment. However, it is very unlikely that the
transition form factors can be enhanced by a factor of within the
ISGW quark model to account for the discrepancy between theory and experiment.
As many of the current data are still preliminary and lack sufficient statistic
significance, more accurate measurements are needed to pin down the issue.Comment: 11 page
Hadronic Charmed Meson Decays Involving Axial Vector Mesons
Cabibbo-allowed charmed meson decays into a pseudoscalar meson and an
axial-vector meson are studied. The charm to axial-vector meson transition form
factors are evaluated in the Isgur-Scora-Grinstein-Wise quark model. The dipole
momentum dependence of the transition form factor and the presence of
a sizable long-distance -exchange are the two key ingredients for
understanding the data of . The mixing angle of
the strange axial-vector mesons is found to be or
from decays. The study of decays excludes the positive mixing-angle
solutions. It is pointed out that an observation of the decay at the level of will rule out
and favor the solution .
Though the decays are color suppressed, they are
comparable to and even larger than the color-allowed counterparts: and . The finite width effect of the axial-vector resonance is
examined. It becomes important for in particular when its width is
near 600 MeV.Comment: 19 page
Charmless Two-body Baryonic B Decays
We study charmless two-body baryonic B decays in a diagramatic approach.
Relations on decay amplitudes are obtained. In general there are more than one
tree and more than one penguin amplitudes. The number of independent amplitudes
can be reduced in the large m_B limit. It leads to more predictive results.
Some prominent modes for experimental searches are pointed out.Comment: 15 pages, 2 figures. To appear in Phys. Rev.
Nonresonant Three-body Decays of D and B Mesons
Nonresonant three-body decays of D and B mesons are studied. It is pointed
out that if heavy meson chiral perturbation theory (HMChPT) is applied to the
heavy-light strong and weak vertices and assumed to be valid over the whole
kinematic region, then the predicted decay rates for nonresonant charmless
3-body B decays will be too large and especially B^- --> pi^- K^+ K^- greatly
exceeds the current experimental limit. This can be understood as chiral
symmetry has been applied there twice beyond its region of validity. If HMChPT
is applied only to the strong vertex and the weak transition is accounted for
by the form factors, the dominant B^* pole contribution to the tree-dominated
direct three-body B decays will become small and the branching ratio will be of
order 10^{-6}. The decay modes B^- --> (K^- h^+ h^-)_{NR} and bar{B}^0 -->
(bar{K}^0 h^+h^-)_{NR} for h = pi, K are penguin dominated. We apply HMChPT in
two different cases to study the direct 3-body D decays and compare the results
with experiment. Theoretical uncertainties are discussed.Comment: 24 pages, 2 figures. New experimental results of direct 3-body D
decays as Reported at ICHEP2002 are included. To appear in Phys. Re
Nonleptonic Weak Decays of Bottom Baryons
Cabibbo-allowed two-body hadronic weak decays of bottom baryons are analyzed.
Contrary to the charmed baryon sector, many channels of bottom baryon decays
proceed only through the external or internal W-emission diagrams. Moreover,
W-exchange is likely to be suppressed in the bottom baryon sector.
Consequently, the factorization approach suffices to describe most of the
Cabibbo-allowed bottom baryon decays. We use the nonrelativistic quark model to
evaluate heavy-to-heavy and heavy-to-light baryon form factors at zero recoil.
When applied to the heavy quark limit, the quark model results do satisfy all
the constraints imposed by heavy quark symmetry. The decay rates and up-down
asymmetries for bottom baryons decaying into and
are calculated. It is found that the up-down asymmetry is negative except for
decay and for decay modes with in the final
state. The prediction for
is consistent with the recent CDF measurement. We also present
estimates for decays and compare with various model
calculations.Comment: 24 pages, to appear in Phys. Rev. Uncertainties with form factor q^2
dependence are discusse
Flavor symmetry analysis of charmless B --> VP decays
Based upon flavor SU(3) symmetry, we perform global fits to charmless
B decays into one pseudoscalar meson and one vector meson in the final
states. We consider different symmetry breaking schemes and find that the one
implied by na{\"i}ve factorization is slightly favored over the exact symmetry
case. The vertex of the unitarity triangle (UT)
constrained by our fits is consistent with other methods within errors. We have
found large color-suppressed, electroweak penguin and singlet penguin
amplitudes when the spectator quark ends up in the final-state vector meson.
Nontrivial relative strong phases are also required to explain the data. The
best-fit parameters are used to compute branching ratio and CP asymmetry
observables in all of the decay modes, particularly those in the decays
to be measured at the Tevatron and LHC experiments.Comment: 23 pages and 2 plots; updated with ICHEP'08 data and expanded in
discussions and reference
Characterization of an endogenous gene expressed in Aedes aegypti using an orally infectious recombinant Sindbis virus
Sindbis virus expression vectors have been used successfully to express and silence genes of interest in vivo in several mosquito species, including Aedes aegypti, Ae. albopictus, Ae. triseriatus,Culex pipiens, Armigeres subalbatus and Anopheles gambiae. Here we describe the expression of an endogenous gene, defensin, in Ae. aegypti using the orally infectious Sindbis virus, MRE/3′2J expression vector. We optimized conditions to infect mosquito larvae per os using C6/36 Ae. albopictus cells infected with the recombinant virus to maximize virus infection and expression of defensin. Infection with the parental Sindbis virus (MRE/3′2J) did not induce defensin expression. Mosquito larvae infected by ingestion of recombinant Sindbis virus-infected C6/36 cells expressed defensin when they emerged as adults. Defensin expression was observed by western analysis or indirect fluorescent assay in all developmental stages of mosquitoes infected with MRE/3′2J virus that contained the defensin insert. The multiplicity of infection of C6/36 cells and the quantity of infected cells consumed by larvae played an important role in defensin expression. Parental viruses, missing the defensin insert, and/or other defective interfering virus may have contributed to these observations
Final-State Phases in Charmed Meson Two-Body Nonleptonic Decays
Observed decay rates indicate large phase differences among the amplitudes
for the charge states in and but
relatively real amplitudes in the charge states for . This
feature is traced using an SU(3) flavor analysis to a sign flip in the
contribution of one of the amplitudes contributing to the latter processes in
comparison with its contribution to the other two sets. This amplitude may be
regarded as an effect of rescattering and is found to be of magnitude
comparable to others contributing to charmed particle two-body nonleptonic
decays.Comment: 19 pages, latex, 4 figures, to be submitted to Phys. Rev.
Final-State Phases in , and Decays
The final-state phases in , and decays
appear to follow a pattern similar to those in , , and decays. Each set of processes is characterized by
three charge states but only two independent amplitudes, so the amplitudes form
triangles in the complex plane. For the first two sets the triangles appear to
have non-zero area, while for the or decays the areas
of the triangles are consistent with zero. Following an earlier discussion of
this behavior for decays, a similar analysis is performed for B decays, and
the relative phases and magnitudes of contributing amplitudes are determined.
The significance of recent results on \ob \to D^{(*)0} \bar{K}^{(*)0} is
noted. Open theoretical and experimental questions are indicated.Comment: 16 pages, LaTeX, 3 figures, to be submitted to Phys. Rev. D.
References added; comments on new experimental results and analysi
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