Interplay between the 02+ resonance and the nonresonant continuum of the drip-line two-neutron halo nucleus 22C

The breakup cross section (BUX) of 22C by 12C at 250 MeV/nucleon is evaluated by the continuum-discretized coupled-channels method incorporating the cluster-orbital shell model (COSM) wave functions. Contributions of the low-lying 02+ and 21+ resonances predicted by COSM to the BUX are investigated. The 21+ resonance gives a narrow peak in the BUX, as in usual resonant reactions, whereas the 02+ resonant cross section has a peculiar shape due to the coupling to the nonresonant continuum, i.e., the background-phase effect (BPE). By changing the scattering angle of 22C after the breakup, a variety of shapes of the 02+ resonant cross sections are obtained. The mechanism of the appearance of the sizable BPE in the breakup of 22C is discussed.