9,487 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 $F_{\pi\gamma}(Q^2)$ 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 $F_{\pi\gamma}(Q^2)$ can provide
helpful information on the pion wavefunction precisely. In this paper, we
present a combined analysis of the data on $F_{\pi\gamma}(Q^2)$ 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 $\beta \in
[0.691,0.757] \rm GeV$ and $B \in [0.00,0.235]$ for $P_{\chi^2} \geq 90\%$,
where $\beta$ and $B$ 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 $\eta_c$, $B_c$ and $\eta_b$. 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
$B_c\to\eta_c$ transition form factor ($f^{B_c\to\eta_c}_+(q^2)$) within the
light-cone sum rules approach, and the results are comparable with other
approaches. It has been found that the twist-3 DAs $\phi^P_{3;\eta_c}$ and
$\phi^\sigma_{3;\eta_c}$ are important for a reliable prediction of
$f^{B_c\to\eta_c}_+(q^2)$. For example, at the maximum recoil region, we have
$f^{B_c\to\eta_c}_+(0) = 0.674 \pm 0.066$, in which those two twist-3 terms
provide $\sim33\%$ and $\sim22\%$ contributions. Also we calculate the
branching ratio of the semi-leptonic decay $B_c \to\eta_c l\nu$ as $Br(B_c
\to\eta_c l\nu) = \left( 9.31^{+2.27}_{-2.01} \right) \times 10^{-3}$.Comment: 12 pages, 16 figure

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