212 research outputs found

### Pion distribution amplitude -- from theory to data

We describe the present status of the pion distribution amplitude as
originated from two sources: (i) a nonperturbative approach, based on QCD sum
rules with nonlocal condensates, and (ii) a NLO QCD analysis of the CLEO data
on F^{\gamma\gamma^*\pi}(Q^2), supplemented by the E791 data on diffractive
dijet production, and the JLab F(pi) data on the pion electromagnetic form
factor.Comment: Invited talk given at the Bogolyubov Conference "Problems of
Theoretical and Mathematical Physics", Moscow--Dubna, Russia, 2--6 September,
2004, and at the International Conference "Quark Confinement and Hadron
Spectrum VI 2004", Villasimius (Cagliary), Sardinia, Italy, 21--25 September,
2004; 5pp., 3 figure

### Tagging the pion quark structure in QCD

We combine the constraints on the pion quark structure available from
perturbative QCD, nonperturbative QCD (nonlocal QCD sum rules and light cone
sum rules) with the analysis of current data on F_{\pi\gamma\gamma^*}(Q^2),
including recent high-precision lattice calculations of the second moment of
the pion's distribution amplitude. We supplement these constraints with those
extracted from the renormalon approach by means of the twist-four contributions
to the pion distribution amplitude in order to further increase stability with
respect to related theoretical uncertainties. We show which regions in the
space of the first two non-trivial Gegenbauer coefficients a_2 and a_4 of all
these constraints overlap, tagging this way the pion structure to the highest
degree possible at present.Comment: V1: 6 pages, 2 figures, 1 table. V2: Two references added with
corresponding insertions in the text. Matches version published in PR

### Pion Form Factor in the NLC QCD SR approach

We present results of a calculation of the electromagnetic pion form factor
within a framework of QCD Sum Rules with nonlocal condensates and using a
perturbative spectral density which includes \mathcal{O}(\alpha_s)
contributions.Comment: 9 pages, 2 figures (embedded). Talk presented by the second author at
the Workshop on Physics of Fundamental Interactions, Institute of High Energy
Physics, Protvino, Russia, 22--25 December 200

### QCD vacuum tensor susceptibility and properties of transversely polarized mesons

We re-estimate the tensor susceptibility of QCD vacuum, $\chi$, and to this
end, we re-estimate the leptonic decay constants for transversely polarized
$\rho$- ,~$\rho'$- and b_1-mesons. The origin of the susceptibility is
analyzed using duality between $\rho$- and b_1- channels in a 2-point
correlator of tensor currents. We confirm the results in Nucl.Phys.
B283(1987)706 for the 2-point correlator of tensor currents and disagree with
Phys.Lett. B395(1997)307 on both OPE expansion and the value of QCD vacuum
tensor susceptibility. Using our value for the latter we determine new
estimations of nucleon tensor charges related to the first moment of the
transverse structure function h_1 of a nucleon.Comment: 11 pages, LATeX2-eps, 1 Table, 2 figures are enclosed as ps-files,
psbox.tex is enclosed as a macros; a comparison with another approach and a
new reference are adde

### New shapes of light-cone distributions of the transversely polarized \rho-mesons

We re-analyze the leading twist light-cone distributions for transversely
polarized \rho-, \rho'- and b_1-mesons in the framework of QCD sum rules with
nonlocal condensates. Using different kinds of sum rules to obtain reliable
predictions, we estimate the 2-, 4-, 6- and 8-th moments for transversely
polarized \rho- and \rho'-meson distributions and re-estimate tensor couplings
f^T_{\rho,\rho',b_1}. We stress that the results of standard sum rules also
support our estimation of the second moment of the transversely polarized
\rho-meson distribution. New models for light-cone distributions of these
mesons are constructed. Phenomenological consequences from these distributions
are briefly discussed. Our results are compared with those found by Ball and
Braun (1996), and the latter is shown to be incomplete.Comment: 18 pages, 7 figures use psbox-macro, 1 table, introduction is
improved, new (7) section with applications to semileptonic B->rho-decay is
added. to appear in Eur. Phys. J.

### Polarized and unpolarized $\mu$-pair meson-induced Drell--Yan production and the pion distribution amplitude

We present a detailed analysis of meson-induced massive lepton (muon)
Drell--Yan production for the process $\pi^{-}N\to\mu^{+}\mu^{-}X$, considering
both an unpolarized nucleon target and longitudinally polarized protons. Using
a QCD framework, we focus on the angular distribution of $\mu^+$, which is
sensitive to the shape of the pion distribution amplitude, the goal being to
test corresponding results against available experimental data. Predictions are
made, employing various pion distribution amplitudes, for the azimuthal angle
dependence of the $\mu^{+}$ distribution in the polarized case, relevant for
the planned COMPASS experiment. QCD evolution is given particular attention in
both considered cases.Comment: V1: 18 pages, 10 figures (48 eps files), 2 tables. V2: one wrong
reference removed, missing reference in text inserted; matches version to
appear in Phys. Rev.

- …