Separated response function ratios in exclusive, forward π(±) electroproduction.

The study of exclusive π± electroproduction on the nucleon, including separation of the various structure functions, is of interest for a number of reasons. The ratio RL=σLπ-/σLπ+ is sensitive to isoscalar contamination to the dominant isovector pion exchange amplitude, which is the basis for the determination of the charged pion form factor from electroproduction data. A change in the value of RT=σTπ-/σTπ+ from unity at small -t, to 1/4 at large -t, would suggest a transition from coupling to a (virtual) pion to coupling to individual quarks. Furthermore, the mentioned ratios may show an earlier approach to perturbative QCD than the individual cross sections. We have performed the first complete separation of the four unpolarized electromagnetic structure functions above the dominant resonances in forward, exclusive π± electroproduction on the deuteron at central Q2 values of 0.6, 1.0, 1.6GeV2 at W=1.95GeV, and Q2=2.45GeV2 at W=2.22GeV. Here, we present the L and T cross sections, with emphasis on RL and RT, and compare them with theoretical calculations. Results for the separated ratio RL indicate dominance of the pion-pole diagram at low -t, while results for RT are consistent with a transition between pion knockout and quark knockout mechanisms. © 2014 American Physical Society.