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peaking of the cross section at Q 2 = 1 . 1 GeV 2 comes from the large longitudinal component in this case. The off- forward region is transverse. This behavior agrees with the results from [25]. As we shall see, the same behavior is observed in the DIS regime at HERMES [7] where the value of W is higher. At HERMES, because of the Regge shrinkage of the π -reggeon exchange and smaller trans- verse component, the forward peak just has a steeper − t -dependence [27]. We now turn to π − production at JLAB. In [25] 

the transverse response dσ$_{T}$/dt in the exclusive reaction n ( γ ∗ , π − ) p was found to be smaller than in the reac- tion p ( γ ∗ , π $^{+}$) n . The present results for the π − channel are parameter free. The u -channel transition form fac- tors, Eq. (44), entering n ( γ ∗ , π − ) p have different behav- ior, since, contrary to the s -channel form factors which depend on ( s, Q $^{2}$) now they depend on u and Q 2 with 

Here we calculate the ratio of π − /π + partial cross sec- tions which is of present interest in the dedicated exper- iments at JLAB [50]. In Figure 10 we show the results for the ratio of longitudinal R$_{L}$ = dσ π − L /dσ π + L (dashed curves) and transverse R$_{T}$ = dσ π − T /dσ π + T (solid curves) cross sections as a function of − t + t$_{min}$ , where − t$_{min}$ denotes the minimum value of t for a given Q 2 and W . The curves have been calculated for the values of 

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W = 1 . 95 GeV (top panels) and W = 2 . 2 GeV (bottom panels). The values of Q 2 vary from Q 2 = 0 . 6 GeV 2 (left top) and Q 2 = 1 GeV 2 (right top) to Q 2 = 1 . 6 GeV 2 (left bottom) and Q 2 = 2 GeV 2 (right bottom). At forward angles the longitudinal ratio R$_{L}$ is close to unity and shows a slow increase followed by a decrease at higher values of − t . On the contrary, the ratio R$_{T}$ is practically constant. For Q 2 = 0 . 6 GeV 2 it is around R$_{T}$ ≃ 0 . 6. With increasing value of Q 2 the ratio R$_{T}$ tends to de- crease further and at Q 2 = 2 GeV 2 it gets R$_{T}$ ≃ 0 . 26. An important mechanism which contributes to the 

π − /π + asymmetry is an exchange of the ρ -trajectory. It is destructive in π − and constructive in π + chan- nels, respectively. In Figure 10 the dash-dotted (longi- tudinal ratio) and dash-dash-dotted curves (transverse ratio) correspond to the results without the exchange of ρ . We conclude that dσ$_{T}$/dt in the π − channel is much smaller than in the π + production. Also the inter- ference cross sections follow this behavior since smaller transverse strength translates into smaller dσ$_{TT}$/dt and dσ$_{LT}$/dt . 

## VIII. p ( γ $^{∗}$, π $^{+}$) n AND n ( γ $^{∗}$, π$^{−}$) p AT DESY 

The early DESY data [13–16] and [12] provide an ac- cess to the p ( γ ∗ , π $^{+}$) n and n ( γ ∗ , π − ) p reactions cross sec- 

