Concerning then−pScattering Cross Section at 24 MeV

Abstract

Recent measurements of the $n-p$ scattering cross section at 24 MeV are compared with the later Yale phenomenological multienergy phase-parameter analysis, ${(\mathrm{Y}-\mathrm{IV})}_{pp+np}$. Good agreement is found for both relative and absolute values. Lack of symmetry in the angular distribution of the differential cross section $\sigma \left(\theta \right)$, expected from the Y-IV phases, fits in with the total cross section and the new relative $\sigma \left(\theta \right)$ measurements. The newer data support the YLAN3M, YLAN4M, Y-IV type of phase-parameter set at energies near 25 MeV, with the rather large absolute value of the negative ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ phase shift $K_1$ and a positive value of the ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-{}_{}{}^3{}_{}{}^{}D_1^{}{}_{}{}^{}$ coupling parameter ${\rho }_1$. No claim is made that there exist no other phase-parameter sets acceptable on the basis of scattering data alone; but since the positive sign of ${\rho }_1$ fits in naturally with the positive sign of the quadrupole moment of the deuteron, and since the low-energy anchor of $K_1$ has been obtained by means of a reasonable potential, the new measurements do not indicate a need for discarding these elementary considerations as approximate guides in phase-parameter analysis. The relative importance of contributions of a few phase parameters is pointed out, with special reference to the fore-aft asymmetry of the angular distribution expected from the Y-IV phase parameters.