Neutron energy-angle distributions from 800 MeV proton-proton inelastic scattering

Complete neutron double differential cross sections, ($\frac{d^2\sigma }{d\Omega \mathrm{dE}}$) ($\theta , E$), have been measured for the reaction $p+p\to n+p+{\pi }^{+}$. Approximately 200 000 events have been collected, resulting in cross sections of approximately 10 percent accuracy. The energy spectrum at all angles shows an enhancement that is consistent with large amounts of ${\Delta }^{++}\mathrm{}\left(1232\right)\mathrm{}$ isobar production followed by the decay ${\Delta }^{++}\to p+{\pi }^{+}$. At the peak of the enhancement $\frac{d^2\sigma }{d\Omega \mathrm{dE}}$ in the c.m. drops smoothly from 50 μb ${\mathrm{sr}}^{-1\mathrm{}}$ Me${\mathrm{V}}^{-1\mathrm{}}$ at 0° to 15 μb ${\mathrm{sr}}^{-1\mathrm{}}$ ${\mathrm{MeV}}^{-1\mathrm{}}$ at 90°. The c.m. angular distributions for fixed $p{\pi }^{+}$ recoil mass are of the form $A+B{cos}^2\theta +C{cos}^4\theta$ with $C$ consistent with zero, in qualitative agreement with the Mandelstam model. Some recent models give reasonable fits to the data with few parameters. The total integrated cross section is found to be $\sigma (pp\to \mathrm{np}{\pi }^{+})=16.0\mathrm{}\pm 1.5$ mb.