Conference paper
Hard exclusive electroproduction of two pions and their resonances
M. V. Polyakov
; Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg 188350, Russia and Institut für Theoretische Physik II, Ruhr-Universität Bochum, D-44780 Bochum, Germany
Abstract
We study the hard exclusive production of two pions in the virtual photon fragmentation region with various invariant masses including the resonance region. The amplitude is expressed in terms of two-pion light-cone distribution amplitudes (2πDA’s). We derive dispersion relations for these amplitudes, which allow to fix them completely in terms of ππ-scattering phases and a few low-energy subtraction constants determined by the effective chiral Lagrangian. Quantitative estimates of the resonance as well ππ background DA’s at low normalization point are made. We also prove a new soft-pion theorem relating two-pion DA’s to the one-pion DA’s. Crossing relations between 2πDA’s and parton distributions in a pion are discussed. We demontrate that by studying the shape of the ππ mass spectra (not absolute cross section!) in a diffractive electroproduction, one can extract the deviation of the meson (π,ρ, etc.) wave functions from their asymptotic form 6z(1 − z) and hence, to get important information about the structure of mesons. We suggest an (alternative to Söding’s) parametrization of ππ spectra which is suitable for large photon virtuality.
Keywords
two-pion production; virtual photon fragmentation; dispersion relations; ππ scattering phases; shape of the ππ mass spectra; structure of mesons
Hrčak ID:
305358
URI
Publication date:
1.6.1999.
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