Abstract:
The differential cross sections for the γn → π -p and the γp → π +n processes were measured at Jefferson Lab. The photon energies ranged from 1.1 to 5.5 GeV, corresponding to center-of-mass energies from 1.7 to 3.4 GeV. The pion center-of-mass angles varied from 50° to 110°. The π - and π + photoproduction data both exhibit a global scaling behavior at high energies and high transverse momenta, consistent with the constituent counting rule prediction and the existing π + data. The data suggest possible substructure of the scaling behavior, which might be oscillations around the scaling value. The data show an enhancement in the scaled cross section at center-of-mass energy near 2.2 GeV The differential cross section ratios [dσ/dt(γn → π -p)/dσ/dt(γp → π +n)] at high energies and high transverse momenta can be described by calculations based on one-hard-gluon-exchange diagrams. ©2005 The American Physical Society.