24 0 0.5 1 1.5 2 -t [GeV$^{2}$] 0 0.1 0.2 A  LU sin( CLAS Regge ( Regge ( + a$_{1}$(1260) Regge ( + a$_{1}$(1260) + partons 0 0.5 1 1.5 2 -t [GeV$^{2}$] JLAB@5.7 GeV p(e,e’ )n n(e,e’ )p JLAB@5.7 GeV FIG. 20: (Color online) Left panel: The beam spin azimuthal moment A sin( φ ) LU in exclusive reaction p ( γ $^{∗}$, π $^{+}$) n as a function of − t . The CLAS/JLAB data [6] were collected for hard scattering kinematics with values of E$_{e}$ = 5 . 77 GeV, Q 2 > 1 . 5 GeV 2 and W 2 > 4 GeV $^{2}$. The dashed curves describe the results (the asymmetry is zero) without the resonance contributions and neglecting the exchange of unnatural parity a$_{1}$ (1260) Regge trajectory. The dash-dotted curves correspond to the addition of the axial-vector a$_{1}$ (1260)-reggeon exchange. The solid curves are the model results and account for the resonance/partonic effects. Right panel: The beam spin azimuthal moment A sin( φ ) LU in exclusive reaction n ( γ $^{∗}$, π$^{−}$) p . The notations for the curves are the same as in the left panel. 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. 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]. The difference between the solid and dashed curves in Figure 21 comes from the contribution of reso- 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 ◦ . 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]. XII. A BENCHMARK FOR JLAB AT 12 GEV: p ( γ $^{∗}$, π $^{+}$) n AT CORNELL