Pion photoproduction on the nucleon

Abstract

The $\gamma n \to \pi^- p$ and $\gamma p \to \pi^+ n$ reactions are essential probes of the transition from meson-nucleon degrees of freedom to quark-gluon degrees of freedom in exclusive processes. The cross sections of these processes are also advantageous, for the investigation of oscillatory behavior around the quark counting prediction, since they decrease relatively slower with energy compared with other photon-induced processes. In this talk, we discuss recent results on the $\gamma p \to \pi^+ n$ and $\gamma n \to \pi^{-}p$ processes from Jefferson Lab experiment E94-104. We also discuss a new experiment in which singles $\gamma p \to \pi^+ n$ measurement from hydrogen, and coincidence $\gamma n \to \pi^{-} p$ measurements at the quasifree kinematics from deuterium for center-of-mass energies between 2.3 GeV to 3.4 GeV in fine steps at a center-of-mass angle of $90^\circ$ are planned. The proposed measurement will allow a detailed investigation of the oscillatory scaling behavior in photopion production processes.