Neutral-Pion Production from Proton-Proton Collisions at 735 MeV

An investigation has been made of the reaction $p+p\to p+p+{\pi }^0$ at an incident proton energy of 735 MeV. The external proton beam of the 184-in. synchrocyclotron bombarded a liquid-hydrogen target. Gamma-ray energy spectra were measured at laboratory angles of 6, 32, and 60 deg with respect to the proton beam. Two high-resolution pair spectrometers were used to make these measurements. Computer codes were used to make all necessary corrections to the data and determine the final spectra. No evidence is found for high-energy gamma rays produced from any source other than neutral-pion decay. The cross section for ${\pi }^0$ production was measured to be 3.46±0.25 mb. By use of the method of least squares, angular and momentum distributions of the neutral pion in the two-proton barycentric system were determined from the photon spectra. The pion angular distribution is given by $\frac{d{\sigma }_{{\pi }^0}}{d\Omega }=\left(\frac{{\sigma }_T}{4\pi }\right)[0.834+0.099(3\mathrm{}{cos}^2\theta )+0.067(5\mathrm{}{cos}^4\theta \left)\right],$ where $\theta$ is the barycentric angle of emission. Pion momentum distributions are given for three angles. The results are shown to give reasonable agreement with the isobar model.