Positive Pion Photoproduction from Hydrogen for Incident Photon Energies 300-750 MeV

The differential cross section for the reaction $\gamma +p\to {\pi }^{+}n$ was measured at 19 photon energies between 300 and 750 MeV in the laboratory frame, for pion angles between 0° and 130° in the c.m. system. The pions were analyzed in angle and momentum with a magnetic spectrometer and detected by a counter telescope. The 0° measurements could be achieved, in spite of the excessive positron rate, owing to a mass-spectrometer arrangement. No direct indication for the electromagnetic excitation of the $P_{11}$ resonance (1466 MeV) was found. Comparison is made with theoretical calculations of ${\pi }^{+}$ photoproduction.