Improved agreement between calculation and ${\pi }^{\pm }$ elastic-scattering data across the (3,3) resonance is obtained by assuming the $\pi$-nucleon collision energy, $\omega$, to be ≃ 30 MeV less than the incident pion energy. This effect has been observed for nuclei ranging from ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ to ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$.

• Received 2 June 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.1828