Photoproduction of π+ mesons from hydrogen

The differential cross section for π+ photoproduction has been determined at 19 points, at center-of-mass angles from 30 to 150 deg, and at photon energies from 162 to 225 MeV. The data are concentrated near 180 MeV, where a full angular distribution has been determined. The relative values of the cross sections are accurate to 5% or better, and the absolute normalization is accurate to 4%. The experiment provides data of improved accuracy which are in general consistent with previous results. The extrapolation to threshold gives a value for (k*/p*)(dσ/dΩ)* at threshold of 16.1±0.7 μb/sr, where k*, p*, and (dσ/dΩ)* are the photon energy, pion momentum, and differential cross section, all in the center-of-mass system.