Determination of the Nucleon-Nucleon Elastic-Scattering Matrix. V. New Results at 25 MeV

Analyses of $N-N$ experiments at 25 MeV have been hampered by a lack of complete scattering data, especially for the scattering states with isotopic spin $T=0\mathrm{}$. In particular, there is an ambiguity in the single-energy $T=0\mathrm{}$ solutions at 25 MeV. This ambiguity, which we discuss here in detail, is partly resolved by the addition of new ($n, p$) data. Some new ($p, p$) data have also been added. The resulting phases more closely resemble the values expected from potential models—with which they are compared. The new selection of data permits a determination of the pion-nucleon coupling constant (${g_{\pi }}^2=14.3\mathrm{}\pm 1.3$), whereas the older selections did not. An investigation of the parabolic approximation for each of the phases indicates the extent to which one can believe the uncertainties as given by an error-matrix calculation. The energy-dependent analyses in this energy region have been improved by having the $S$ phases extrapolate to the scattering length and effective-range expansions at low energies. The resulting phases give excellent fits to the data at 10 MeV as well as at 25 MeV. Experiments that would further improve the analysis at 25 MeV are suggested. The present results are in some disagreement with a recently released Dubna analysis at 23 MeV.