Neutron spectra at 0° from proton-proton collisions between 647 and 805 MeV

Momentum spectra of neutrons at 0\ifmmode^\circ\else\textdegree\fi{} from the process $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{np}{\ensuremath{\pi}}^{+}$ have been measured at 647, 771, and 805 MeV. Absolute cross sections $\frac{{d}^{2}\ensuremath{\sigma}}{d\ensuremath{\Omega}\mathrm{dp}}$ and $\frac{d\ensuremath{\sigma}}{d{\ensuremath{\Omega}}^{*}}$ are given for all three energies. A phenomenological calculation using only $S$- and $P$-wave $\ensuremath{\pi}N$ phase shifts and an $NN$ final-state interaction appears to account for the shapes and magnitudes of the spectra quite well. Comparison with the process $\mathrm{np}\ensuremath{\rightarrow}pX$ indicates a non-negligible contribution from nonresonant amplitudes.