3,468 research outputs found
On the Unitarity Triangles of the CKM Matrix
The unitarity triangles of the Cabibbo-Kobayashi-Maskawa (CKM)
matrix are studied in a systematic way. We show that the phases of the nine CKM
rephasing invariants are indeed the outer angles of the six unitarity triangles
and measurable in the -violating decay modes of and mesons.
An economical notation system is introduced for describing properties of the
unitarity triangles. To test unitarity of the CKM matrix we present some
approximate but useful relations among the sides and angles of the unitarity
triangles, which can be confronted with the accessible experiments of quark
mixing and violation.Comment: 9 Latex pages; LMU-07/94 and PVAMU-HEP-94-5 (A few minor changes are
made, accepted for publication in Phys. Lett. B
The longitudinal and transverse distributions of the pion wavefunction from the present experimental data on the pion-photon transition form factor
It is noted that the low-energy behavior of the pion-photon transition form
factor is sensitive to the transverse distribution of the
pion wavefunction, and its high-energy behavior is sensitive to the
longitudinal one. Thus a careful study on can provide
helpful information on the pion wavefunction precisely. In this paper, we
present a combined analysis of the data on reported by the
CELLO, the CLEO, the BABAR and the BELLE collaborations. It is performed by
using the method of least squares. By using the combined measurements of BELLE
and CLEO Collaborations, the pion wavefunction longitudinal and transverse
behavior can be fixed to a certain degree, i.e. we obtain and for ,
where and are two parameters of a convenient pion wavefunction
model whose distribution amplitude can mimic the various longitudinal behavior
under proper choice of parameters. We observe that the CELLO, CLEO and BELLE
data are consistent with each other, all of which prefers the asymptotic-like
distribution amplitude; while the BABAR data prefers a more broad distribution
amplitude, such as the CZ-like one.Comment: 7 pages, 10 figure
Heavy Pseudoscalar Twist-3 Distribution Amplitudes within QCD Theory in Background Fields
In this paper, we study the properties of the twist-3 distribution amplitude
(DA) of the heavy pseudo-scalars such as , and . New sum
rules for the twist-3 DA moments \left_{\rm HP} and
\left_{\rm HP} up to sixth orders and up to dimension-six
condensates are deduced under the framework of the background field theory.
Based on the sum rules for the twist-3 DA moments, we construct a new model for
the two twist-3 DAs of the heavy pseudo-scalar with the help of the
Brodsky-Huang-Lepage prescription. Furthermore, we apply them to the
transition form factor () within the
light-cone sum rules approach, and the results are comparable with other
approaches. It has been found that the twist-3 DAs and
are important for a reliable prediction of
. For example, at the maximum recoil region, we have
, in which those two twist-3 terms
provide and contributions. Also we calculate the
branching ratio of the semi-leptonic decay as .Comment: 12 pages, 16 figure
from the semileptonic decay and the properties of the meson distribution amplitude
The improved QCD light-cone sum rule (LCSR) provides an effective way to deal
with the heavy-to-light transition form factors (TFFs). Firstly, we adopt the
improved LCSR approach to deal with the TFF up to twist-4
accuracy. Due to the elimination of the most uncertain twist-3 contribution and
the large suppression of the twist-4 contribution, the obtained LCSR shall
provide us a good platform for testing the -meson leading-twist DA. For the
purpose, we suggest a new model for the -meson leading-twist DA
(), whose longitudinal behavior is dominantly determined by a
parameter . Moreover, we find its second Gegenbauer moment .
Varying within certain region, one can conveniently mimic the -meson DA
behavior suggested in the literature. Inversely, by comparing the estimations
with the experimental data on the -meson involved processes, one can get a
possible range for the parameter and a determined behavior for the
-meson DA. Secondly, we discuss the TFF at the maximum recoil
region and present a detailed comparison of it with the pQCD estimation and the
experimental measurements. Thirdly, by applying the LCSR on , we
study the CKM matrix element \Vcb together with its uncertainties by adopting
two types of processes, i.e. the -type and the -type.
It is noted that a smaller shows a better agreement with the
experimental value on \Vcb. For example, for the case of , we obtain
and , whose first (second)
uncertainty comes from the squared average of the mentioned theoretical
(experimental) uncertainties.Comment: 13 pages, 10 figures. Reference updated and discussion improved. To
be published in Nucl.Phys.
Twist-3 light-cone distribution amplitudes of the scalar mesons within the QCD sum rules and their application to the transition form factors
We investigate the twist-3 light-cone distribution amplitudes (LCDAs) of the
scalar mesons , and within the QCD sum rules. The QCD
sum rules are improved by a consistent treatment of the sizable -quark mass
effects within the framework of the background field approach. Adopting the
valence quark component as the dominant structure of the
scalar mesons, our estimation for their masses are close to the measured
, and . From the sum rules, we obtain
the first two non-zero moments of the twist-3 LCDAs :
and ; those of the twist-3 LCDAs
: and ; and those of the twist-3 LCDAs :
and , respectively. As an
application of those twist-3 LCDAs, we study the transition form
factors by introducing proper chiral currents into the correlator, which is
constructed such that the twist-3 LCDAs give dominant contribution and the
twist-2 LCDAs make negligible contribution. Our results of the
transition form factors at the large recoil region are
consistent with those obtained in the literature, which inversely shows the
present twist-3 LCDAs are acceptable.Comment: 14 pages, 12 figures, 7 table
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