Exclusive channels in semi-inclusive production of pions and kaons
  We investigate the role of exclusive channels in semi-inclusive electroproduction of pions and kaons. Using the QCD factorization theorem for hard exclusive processes we evaluate the cross sections for exclusive pseudoscalar and vector meson production in terms of generalized parton distributions and meson distribution amplitudes. We investigate the uncertainties arising from the modeling of the nonperturbative input quantities. Combining these results with available experimental data, we compare the cross sections for exclusive channels to that obtained from quark fragmentation in semi-inclusive deep inelastic scattering. We find that rho^0 production is the only exclusive channel with significant contributions to semi-inclusive pion production at large z and moderate Q^2. The corresponding contribution to kaon production from the decay of exclusively produced phi and K^* is rather small. 
M. Diehl, W. Kugler, A. Schaefer, C. Weiss