Undamped Surface Waves in the Scattering ofO16+Si28atEc.m.=35MeV

The elastic scattering of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=35\mathrm{}$ MeV has been measured in the angular range $20°<~{\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~180°$. The data exhibit a strongly oscillatory behavior in the region $60°<{\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~180°$ and a pronounced backward rise up to $\frac{d\sigma }{d{\sigma }_{\mathrm{Ruth}}}\left(180\mathrm{}°\right)\approx 1.5\times {10}^{-2\mathrm{}}$. The structure at backward angles is of the form of a Legendre polynomial ${\left|P_{l=26\mathrm{}}\right(cos\theta \left)\right|}^2$, indicating the existence of a partial-wave (orbiting) resonance.