212 research outputs found

    Pion distribution amplitude -- from theory to data

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    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

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    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

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    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

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    We re-estimate the tensor susceptibility of QCD vacuum, χ\chi , and to this end, we re-estimate the leptonic decay constants for transversely polarized ρ\rho - ,~ρ\rho'- and b_1-mesons. The origin of the susceptibility is analyzed using duality between ρ\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

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    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 μ\mu-pair meson-induced Drell--Yan production and the pion distribution amplitude

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    We present a detailed analysis of meson-induced massive lepton (muon) Drell--Yan production for the process πNμ+μX\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 μ+\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 μ+\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.