0 90 180 270 360  [deg] 0 2 4 6 0 90 180 270 360  [deg] 0 3 6 9 0 90 180 270 360  [deg] 0 5 10 15 20 25 0 90 180 270 360  [deg] 0 10 20 30 40 50 2  d 2 /dt d b/GeV 2 ] Q$^{2}$= 1.59 GeV 2 W = 2.21 GeV JLAB = 0.58 = 0.33 = 0.23 = 0.55 Q$^{2}$= 1.94 GeV 2 t = - 0.139 GeV 2 t = - 0.145 GeV 2 W = 2.27 GeV JLAB = 0.74 JLAB = 0.37 Q$^{2}$= 0.6 GeV 2 t = - 0.05 GeV 2 W = 1.95 GeV = 0.31 Q$^{2}$= 1 GeV 2 t = - 0.12 GeV 2 W = 1.95 GeV JLAB = 0.62 14 FIG. 8: (Color online) φ dependence of the differential cross sections 2 π d $^{2}$σ/dtdφ in exclusive reaction p ( γ $^{∗}$, π $^{+}$) n at fixed ( − t, Q $^{2}$, W ) and two (high and low) values of ε . The notations for the curves are the same as in Figure 6. The upper set of solid, dashed and dash-dotted curves belong to the higher value of ε . The experimental data are from Refs. [1–3]. dσ$_{LT}$/dt changes sign to positive and dσ$_{TT}$/dt gets large and negative. The contribution of resonances to the lon- gitudinal cross section dσ$_{L}$/dt is sizable at forward an- gles where the pion form factor is extracted [5] and in- creases with increasing value of Q $^{2}$. However, the ef- fect is particularly pronounced in dσ$_{T}$/dt and interfer- ence cross sections dσ$_{TT}$/dt and dσ$_{LT}$/dt . For instance, at Q 2 = 2 . 45 GeV 2 and Q 2 = 3 . 91 GeV 2 dσ$_{T}$/dt has been increased by about two orders of magnitude. Λ 2 γππ = 0 . 46 GeV $^{2}$. In Figure 6 the dashed curves de- scribe this contribution. As one can see, the steep fall of dσ$_{L}$/dt away from forward angles comes entirely from the rapidly decreasing π -exchange amplitude. The π - exchange practically saturates the longitudinal response dσ$_{L}$/dt . At these values of Q 2 > 1 . 5 GeV 2 the contri- bution of the π -reggeon exchange to the transverse cross section dσ$_{T}$/dt is already marginal. The π -exchange is effective in the interference cross sections. However, ex- perimentally the cross section dσ$_{TT}$/dt is negative and dσ$_{LT}$/dt is positive. The exchange of π contributes here just with opposite signs. The histograms in Figure 6 for dσ$_{T}$/dt are from [25]. The assumption used in Ref. [25] for γ ∗ p → π $^{+}$n is that at the invariant masses reached at JLAB nucleon reso- nances can contribute to the 1 π channel as well. Then similar to the use of Regge trajectories in the t -channel that takes higher meson excitations into account one has to consider the direct hard interaction of virtual pho- tons with partons (DIS) since DIS involves all possible transitions of the nucleon from its ground state to any excited state [51]. Modeling the resonance contributions by DIS like processes, followed by hadronization into the π $^{+}$n channel, result in histograms shown in Figure 6. Our present treatment of resonance contributions pro- duces a result which is very close to that obtained in our previous work [25]. However, the present approach goes beyond the two-component hadron-parton model of Ref. [25] and allows to study the interference and non- π - pole background effects on the amplitude level. We gauge the π -exchange by adding the nucleon-pole term. The exchanges of ρ (770) /a$_{2}$ (1320) and a$_{1}$ (1260) Regge trajectories are also added. This result corre- sponds to the dash-dotted curves in Figure 6. As one can see, the longitudinal cross sections dσ$_{L}$/dt is barely changed. The transverse cross section dσ$_{T}$/dt is negligi- bly small but finite at forward angles. The sign of the interference cross section dσ$_{TT}$/dt now respects the ex- perimental data but the magnitude of the cross section is compatible with zero. The cross section dσ$_{LT}$/dt has been increased by about a factor of two but is still largely negative. The transverse dσ$_{T}$/dt component is insensitive to the variation of the cut-off in the pion form factor Λ$_{γππ}$. On the contrary, the magnitude of dσ$_{L}$/dt is driven by this parameter. In Figure 7 we compare the model re- sults with data measured at lower values of ( Q $^{2}$, W ) in the F π -1 experiment [2]. The calculations are per- In the last step we use the r/p -transition form fac- tor to include the effect of resonances. The solid curves in Figure 6 correspond to this description. As one can see, all the cross sections are now very well described. Furthermore, the magnitude of dσ$_{T}$/dt is strongly corre- lated with the sign and magnitude of the interference cross sections dσ$_{TT}$/dt and dσ$_{LT}$/dt . The description of dσ$_{T}$/dt translates at once into a remarkable descrip- tion of both interference cross sections. For instance,