Search for α condensed states in 13C using α inelastic scattering

We searched for the α condensed state in 13C by measuring the α inelastic scattering at Eα = 388 MeV at forward angles including 0 degrees. We performed the distorted wave Born-approximation calculation with the single-folding potential and the multipole decomposition analysis to determine the isoscalar transition strengths in 13C. We found a bump structure around Ex = 12.5 MeV consisting of several 1/2− states, which were excited by the isoscalar monopole (IS0) transitions from the ground state. We proposed that this bump was due to the mirror state of the 13.5 MeV-state in 13N, which dominantly decayed to the α condensed state in 12C. Although this bump was speculated to be a candidate for the α condensed state, the OCM calculation suggested that the α condensed state is unlikely to emerge as the negative parity states. We also found two 1/2+ or 3/2+ states at Ex = 14.5 and 16.1 MeV excited by the isoscalar dipole (IS1) transitions. We compared the experimental level diagram and the IS0 and IS1 transitions strengths with those predicted by shell-model and cluster-model calculations. We suggested that the 16.1-MeV state is a possible candidate for the α condensed state predicted by the cluster-model calculations. 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 α condensed state in 13C.