Neutron Deformation Parameter from Comparative Study ofπ+andπ−Inelastic Scattering

Differential cross sections for the excitation of the $2^{+}$ state in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ by 230-MeV pions are found to be about 70% larger for ${\pi }^{-}$ than for ${\pi }^{+}$. Since the $\pi$-nucleon interaction at this energy is dominated by the (3,3) resonance, it is concluded that the results imply that ${〈\beta R〉}_n\approx 1.3{〈\beta R〉}_p$, or alternatively, that ${\left(\beta R\right)}_n \left(\mathrm{valence}\mathrm{neutrons}\right)\approx 3{\left(\beta R\right)}_c\left(\mathrm{core}\right)$, where $\beta$ is the deformation parameter and $R$ the equilibrium radius of the deformed potential. We believe that these results constitute the first example of measurement of the neutron deformation parameter.