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vector a$_{1}$ (1260) is small. However, as one can see, the contribution of a$_{1}$ (1260) is important in the polarization observables. For instance, a strong interference pattern of the a$_{1}$ (1260)-reggeon exchange makes the polarization observables, like the beam SSA, very sensitive to the dif- ferent scenarios [45] describing the structure and behav- ior of a$_{1}$ (1260) in high- Q 2 processes. 

In the last step we account for the r/p -contribution. The latter strongly influence the asymmetry parameter A sin( φ ) LU . The model results (solid curves) are in agreement with the positive A sin( φ ) LU in the π + channel and predict much smaller A sin( φ ) LU in the π − channel. A sizable and positive A sin( φ ) LU has been also observed at HERMES in π + SIDIS close to the exclusive limit z → 1 [59]. 

## XII. A BENCHMARK FOR JLAB AT 12 GEV: p ( γ $^{∗}$, π $^{+}$) n AT CORNELL 

A forthcoming upgrade of the JLAB to 12 GeV will allow to measure p ( e, e ′ π $^{+}$) n and n ( e, e ′ π − ) p reactions for values of Q 2 = 1 . 6 ÷ 6 . 0 GeV 2 and W near 3 GeV [56]. 

This is just an intermediate region between the present JLAB and the deep exclusive HERMES data. In this ( Q $^{2}$, W ) region there are old Cornell data [10] around W ≃ 3 . 1 GeV and values of Q 2 ≃ 1 . 2 and 1.7 GeV $^{2}$. These data may serve as a benchmark for the JLAB at 12 GeV predictions. 

Figure 21 shows the Cornell data [10] and the calcu- lated differential cross sections for the electroproduction of π + meson as a function of − t . As an example, we selected data with the virtual-photoproduction planes of the emitted pions in average parallel − 45 ◦ < φ < 45 ◦ to the electron scattering plane. The solid curves in Fig- ure 21 describe the model results and the dashed curves correspond to the results without the resonance contri- butions. The cross sections have been integrated over the corresponding range of azimuthal out-of-plane an- gles. Figure 22 shows the calculated ratio of π − and π + differential cross sections (solid curve) as a function of − t . The data are from [10]. As in Figure 21 the cross sections have been integrated over the range of azimuthal out-of-plane acceptance − 45 ◦ < φ < 45 ◦ . The difference between the solid and dashed curves 

in Figure 21 comes from the contribution of reso- 

