Backward pion photoproduction

TL;DR

This paper analyzes backward pion photoproduction using Regge phenomenology at high energies, comparing with experimental data, and discusses the energy range where Regge behavior becomes apparent.

Contribution

It applies Regge theory systematically to backward pion photoproduction and compares predictions with recent experimental data, identifying the energy range for Regge limit realization.

Findings

Regge model describes high-energy backward pion photoproduction well above 3 GeV.

No clear convergence to Regge predictions below 2.5 GeV.

Baryon trajectories align with known excited baryon spectra.

Abstract

We present a systematic analysis of backward pion photoproduction for the reactions gamma p -> pi0 p and gamma p -> pi+ n. Regge phenomenology is applied at invariant collision energies above 3 GeV in order to fix the reaction amplitude. A comparision with older data on pi0- and pi+ photoproduction at theta = 180 degrees 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} < 2.5 GeV, covered by the new measurements of gamma p -> pi0 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.