Evaluate the P-wave phase shift δ1 for scattering from a hard sphere, for which the potential energy is given by
V(r)={∞0r<ar>a
Express your result in terms of j1(ka) and η1(ka). Use the leading behavior of j1(ρ) and η1(ρ) for small ρ to show that δ1→−(ka)3/3 as ka→0, and thus δ1 can indeed be neglected in comparison to δ0 [see (13.81)] at sufficiently low energy.