22 10 -3 10 -2 10 -1 10 0 10 1 10 2 d L  /dt [ b/GeV 2 ] JLAB 0 2 4 6 8 10 Q$^{2}$ [GeV$^{2}$] 10 -3 10 -2 10 -1 10 0 10 1 d T  /dt [ b/GeV 2 ] JLAB 0 2 4 6 8 10 Q$^{2}$ [GeV$^{2}$] x$_{B}$ = 0.311 x$_{B}$ = 0.451 -t = 0.408 GeV 2 -t = 0.145 GeV 2 0 3 6 9 12 15 Q$^{2}$ [GeV$^{2}$] 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 [d L /dt] / [d σ$^{T}$  /dt] x$_{B}$ = 0.311 x$_{B}$ = 0.451 x$_{B}$ = 0.8 x$_{B}$ = 0.6 x$_{B}$ = 0.1 x$_{B}$= 0.65  forward production  x$_{B}$ = 0.75 FIG. 18: (Color online) The Q 2 dependence of the ratio of lon- gitudinal dσ$_{L}$/dt to transverse dσ$_{T}$/dt differential cross sec- tions in the forward π + production. The different curves cor- respond to different values of Bjorken scaling variable x$_{B}$ . FIG. 17: (Color online) Q 2 dependence of the longitudin al dσ$_{L}$/dt (top panels) and transverse dσ$_{T}$/dt (bottom panel s) cross sections in p ( γ $^{∗}$, π $^{+}$) n reaction at fixed values of − t and Bjorken x$_{B}$ . The solid curves are the model predictions for the scaling curves. The dashed curves correspond to the con- tribution of the π -reggeon exchange alone. The dash-dotted curves are the model results without the contributions of res- onances. The experimental data are from Ref. [3]. curves correspond to different values of x$_{B}$ . All the curves start at the value of W ≃ 1 . 9 GeV. For small and inter- mediate values of x$_{B}$ the model results show an increase of the ratio dσ$_{L}$/dσ$_{T}$ as a function of Q $^{2}$. Only at small values of Bjorken x$_{B}$ the ratio dσ$_{L}$/dσ$_{T}$ is qualitatively in agreement with the predicted ∼ Q 2 behavior. In the valence quark region above x$_{B}$ ≃ 0 . 6 the cross section ra- tio scales and is actually independent of the value of Q $^{2}$. In this region the transverse component σ$_{T}$ dominates the π + electroproduction cross section. In the experi- mental determination of the pion transition form factor from forward σ$_{L}$ data one can, therefore, better isolate the longitudinal response by minimizing the Bjorken x$_{B}$ . we check this predicted σ$_{L}$/σ$_{T}$ ∼ Q 2 scaling within our model calculations. In Section IX we concluded that the physics content of the HERMES deep exclusive p ( γ ∗ , π $^{+}$) n data is es- sentially the same as at JLAB. Figure 19 shows the Q 2 dependence of the measured cross sections in DIS for dif- ferent x$_{B}$ bins [7, 57]. These are the same data sets from HERMES (see previous section) integrated over − t . The Q 2 dependence of the experimental data is well described by the calculations (solid curves) from the present model. The dashed and dash-dotted curve describe the longitudi- In Figure 17 we show our results for the Q 2 depen- dence of p ( γ ∗ , π $^{+}$) n reaction cross sections dσ$_{L}$/dt and dσ$_{T}$/dt at fixed − t and Bjorken variable x$_{B}$ . The ex- perimental data are from Ref. [3] and correspond to the forward π + production. The solid curves are the model predictions and describe the available data very well. The dashed curves describe the contribution of the π -reggeon exchange to the Q 2 scaling curves only. The dash-dotted curves are the model results without the resonance con- tributions. The latter effect is again large in the trans- verse cross section and gives only small correction to the longitudinal cross section dσ$_{L}$/dt . The Q 2 dependence of dσ$_{L}$/dt is essentially driven by the pion form factor. The Q 2 dependence of the ratio of longitudinal dσ$_{L}$/dt to transverse dσ$_{T}$/dt differential cross sections for the for- ward π + production is shown in Figures 18. The different B. HERMES data A. JLAB data