Generalized counting rule and oscillatory scaling
We studied the energy dependence of the pp elastic scattering data and the pion-photoproduction data at a 90° c.m. angle in light of the new generalized counting rale derived for exclusive processes. We show that by including the helicity-nonconserving amplitudes and their interference with the Landshoff amplitude, we are able to reproduce the energy dependence of all the pp elastic cross-section and spin-correlation (AN N) data available above the resonance region. The pion-photoproduction data can also be described by this approach; however, data with much finer energy spacing are needed to confirm the oscillations about the scaling behavior. This study strongly suggests an important role for helicity-nonconserving amplitudes related to the quark orbital angular momentum and for the interference of these amplitudes with the Landshoff amplitude at GeV energies. © 2005 The American Physical Society.
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