1,449 research outputs found
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.
The -meson longitudinal leading-twist distribution amplitude
In the present paper, we suggest a convenient model for the vector
-meson longitudinal leading-twist distribution amplitude
, whose distribution is controlled by a single parameter
. By choosing proper chiral current in the correlator, we obtain
new light-cone sum rules (LCSR) for the TFFs , and ,
in which the -order provides dominant
contributions. Then we make a detailed discussion on the
properties via those TFFs. A proper choice of can
make all the TFFs agree with the lattice QCD predictions. A prediction of
has also been presented by using the extrapolated TFFs, which
indicates that a larger leads to a larger . To
compare with the BABAR data on , the longitudinal leading-twist
DA prefers a doubly-humped behavior.Comment: 7 pages, 3 figures. Discussions improved and references updated. To
be published in Phys.Lett.
Preliminary Functional-Structural Modeling on Poplar (Salicaceae)
Poplar is one of the best fast-growing trees in the world, widely used for
windbreak and wood product. Although architecture of poplar has direct impact
on its applications, it has not been descried in previous poplar models,
probably because of the difficulties raised by measurement, data processing and
parameterization. In this paper, the functional-structural model GreenLab is
calibrated by using poplar data of 3, 4, 5, 6 years old. The data was acquired
by simplifying measurement. The architecture was also simplified by classifying
the branches into several types (physiological age) using clustering analysis,
which decrease the number of parameters. By multi-fitting the sampled data of
each tree, the model parameters were identified and the plant architectures at
different tree ages were simulated
Excited Heavy Quarkonium Production at the LHC through -Boson Decays
Sizable amount of heavy-quarkonium events can be produced through -boson
decays at the LHC. Such channels will provide a suitable platform to study the
heavy-quarkonium properties. The "improved trace technology", which disposes
the amplitude at the amplitude-level, is helpful for deriving
compact analytical results for complex processes. As an important new
application, in addition to the production of the lower-level Fock states
and , we make a further study on the
production of higher-excited -quarkonium Fock states
, and . Here
stands for the -charmonium,
-quarkonium and -bottomonium respectively. We show
that sizable amount of events for those higher-excited states can also be
produced at the LHC. Therefore, we need to take them into consideration for a
sound estimation.Comment: 7 pages, 9 figures and 6 tables. Typo errors are corrected, more
discussions and two new figures have been adde
Degeneracy Relations in QCD and the Equivalence of Two Systematic All-Orders Methods for Setting the Renormalization Scale
The Principle of Maximum Conformality (PMC) eliminates QCD renormalization
scale-setting uncertainties using fundamental renormalization group methods.
The resulting scale-fixed pQCD predictions are independent of the choice of
renormalization scheme and show rapid convergence. The coefficients of the
scale-fixed couplings are identical to the corresponding conformal series with
zero -function. Two all-orders methods for systematically implementing
the PMC-scale setting procedure for existing high order calculations are
discussed in this article. One implementation is based on the PMC-BLM
correspondence \mbox{(PMC-I)}; the other, more recent, method \mbox{(PMC-II)}
uses the -scheme, a systematic generalization of the minimal
subtraction renormalization scheme. Both approaches satisfy all of the
principles of the renormalization group and lead to scale-fixed and
scheme-independent predictions at each finite order. In this work, we show that
PMC-I and PMC-II scale-setting methods are in practice equivalent to each
other. We illustrate this equivalence for the four-loop calculations of the
annihilation ratio and the Higgs partial width . Both methods lead to the same resummed (`conformal') series up to
all orders. The small scale differences between the two approaches are reduced
as additional renormalization group -terms in the pQCD expansion
are taken into account. We also show that {\it special degeneracy relations},
which underly the equivalence of the two PMC approaches and the resulting
conformal features of the pQCD series, are in fact general properties of
non-Abelian gauge theory.Comment: 7 pages, 1 figur
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