Evidence for strong refraction of ${}^3$He in an alpha-particle condensate

Abstract

We have analyzed ${}^3$He scattering from ${}^{12}$C at 34.7 and 72 MeV in a coupled channel method with a double folding potential derived from the precise wave functions for the ground 0${}^{+}$ state and $0_2^{+}$ (7.65 MeV) Hoyle state, which has been suggested to be an $\alpha$ particle condensate. It is found that strong refraction of ${}^3$He in the Hoyle state can be clearly seen in the experimental angular distribution at {\it low} incident energy region as an Airy minimum of the {\it pre-rainbow oscillations}.