Amplitudes and Model forπNBackward Scattering at 6GeVc

Using reasonable assumptions concerning the $s$-channel helicity-nonflip amplitude $M_{++}^{\frac{3}{2}}$ of isospin $\frac{3}{2}$ in the $u$ channel and the helicity-flip amplitude $M_{+-}^{\frac{1}{2}}$, we extract from the data at 6 $\frac{\mathrm{GeV}}{c}$ on $\pi N$ backward scattering the remaining amplitudes. We find that the isospin-$\frac{3}{2}$ amplitudes can be described in a Regge-pole model with absorption. A description of $M^{\frac{1}{2}}$ amplitudes is given, using degenerate $N_{\alpha }$ and $N_{\gamma }$ trajectories. The $N_{\gamma }$ couplings are found to be fairly important, especially in the $M_{++}^{\frac{1}{2}}$ amplitude which then has to be strongly absorbed.