Backward pion photoproduction

Abstract

We present a systematic analysis of backward pion photoproduction for the reactions $\gamma$ p $\rightarrow$ $\pi^{0}_{}$ p and $\gamma$ p $\rightarrow$ $\pi^{+}_{}$ n . Regge phenomenology is applied at invariant collision energies above 3GeV in order to fix the reaction amplitude. A comparision with older data on $\pi^{0}_{}$ - and $\pi^{+}_{}$ -photoproduction at $\vartheta$ = 180° indicates that the high-energy limit as given by the Regge calculation could be reached possibly at energies of around $\sqrt{{s}}$ ≃ 3 GeV. In the energy region of $\sqrt{{s}}$ $\le$2.5 GeV, covered by the new measurements of $\gamma$ p $\rightarrow$ $\pi^{0}_{}$ p differential cross-sections at large angles at ELSA, JLab, and LEPS, we see no clear signal for a convergence towards the Regge results. The baryon trajectories obtained in our analysis are in good agreement with those given by the spectrum of excited baryons