Search for alpha condensed states in C-13 using alpha inelastic scattering

We searched for the alpha condensed state in C-13 by measuring the alpha inelastic scattering at E-alpha = 388 MeV at forward angles including 0 degrees. We performed a distorted-wave Born approximation calculation with the single-folding potential and multipole decomposition analysis to determine the isoscalar transition strengths in C-13. We found a bump structure around E-x = 12.5 MeV due to the isoscalar monopole (IS0) transition. A peak-fit analysis suggested that this bump consisted of several 1/2(-) states. We propose that this bump is due to the mirror state of the 13.5 MeV state in N-13, which dominantly decays to the alpha condensed state in C-12. It was speculated that the 1/2(-) states around E-x = 12.5 MeV were candidates for the alpha condensed state, but the 3 alpha + n orthogonality condition model suggests that the alpha condensed state is unlikely to emerge as the negative parity states. We also found two 1/2(+) or 3/2(+) states at E-x = 14.5 and 16.1 MeV excited with the isoscalar dipole (IS1) strengths. We suggest that the 16.1 MeV state is a possible candidate for the alpha condensed state predicted by the cluster model calculations on the basis of the good correspondence between the experimental and calculated level structures. However, the theoretical IS1 transition strength for this state is significantly smaller than the measured value. Further experimental information is strongly desired to establish the alpha condensed state in C-13.