Interplay between the $0_2^{+}$ resonance and the nonresonant continuum of the drip-line two-neutron halo nucleus ${}^{22}$C

The breakup cross section (BUX) of ${}^{22}$C by ${}^{12}$C 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 $0_2^{+}$ and $2_1^{+}$ resonances predicted by COSM to the BUX are investigated. The $2_1^{+}$ resonance gives a narrow peak in the BUX, as in usual resonant reactions, whereas the $0_2^{+}$ 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 ${}^{22}$C after the breakup, a variety of shapes of the $0_2^{+}$ resonant cross sections are obtained. The mechanism of the appearance of the sizable BPE in the breakup of ${}^{22}$C is discussed.

Figure 1

Double differential breakup cross section (DDBUX) of ${}^{22}$C by ${}^{12}$C at 250 MeV/nucleon.

Figure 2

Breakup energy distribution corresponding to $\theta =0^{\circ }$–$0.1^{\circ }$ and its resonant and nonresonant components. See the text for details.

Figure 3

(a) The $0_2^{+}$ DDBUX and (b) the total $0^{+}$ DDBUX. All results except for $\theta =0.{00}^{\circ }$ are multiplied by the numbers beside the lines.