2,337 research outputs found
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
Pion Electromagnetic Form Factor in the Factorization Formulae
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC
wavefunction affects the hard and soft contributions substantially. A model for
the twist-3 wavefunction of the pion has been
constructed based on the moment calculation by applying the QCD sum rules,
whose distribution amplitude has a better end-point behavior than that of the
asymptotic one. With this model wavefunction, the twist-3 contributions
including both the usual helicity components () and the
higher helicity components () to the pion form
factor have been studied within the modified pQCD approach. Our results show
that the twist-3 contribution drops fast and it becomes less than the twist-2
contribution at . The higher helicity components in the
twist-3 wavefunction will give an extra suppression to the pion form factor.
When all the power contributions, which include higher order in ,
higher helicities, higher twists in DA and etc., have been taken into account,
it is expected that the hard contributions will fit the present experimental
data well at the energy region where pQCD is applicable.Comment: 4 pages, 2 figures, Prepared for International Conference on QCD and
Hadronic Physics, Beijing, China, 16-20 June 200
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
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