Evidence of strong dynamic core excitation in ${}^{19}\mathrm{C}$ resonant break-up

The resonant breakup of ${}^{19}\mathrm{C}$ on protons measured at RIKEN [Y. Satou et al., Phys. Lett. B 660, 320 (2008)] is analyzed in terms of a valence-core model for ${}^{19}\mathrm{C}$ that includes possible core excitations. The analysis of the angular distribution of a prominent peak appearing in the relative-energy spectrum could be well described with this model and is consistent with the previous assignment of $5/2^{+}$ for this state. Inclusion of core-excitation effects are found to be essential to giving the correct magnitude of the cross section for this state. By contrast, the calculation assuming an inert ${}^{18}\mathrm{C}$ core is found to largely underestimate the data.

Figure 1

Experimental (far left column) [29, 33] and calculated spectrum of ${}^{19}\mathrm{C}$ in a shell-model calculation with oxbash using the WBP interaction [40, 41] (middle right column), and within a semimicroscopic core-plus-valence-particle calculation (P-AMD, far right column) which takes into account core excitations as described in [34]. We include a second experimental spectrum (middle left column) due to the discrepancy raised by the latest knock-out experiments [30, 31, 32].

Figure 2

Angular distribution of the resonant breakup of ${}^{19}\mathrm{C}$ on protons at 70 MeV/nucleon. The solid red line and the dashed blue line correspond to the XCDCC calculation for the first and the second $5/2^{+}$ resonance of the P-AMD model [34] respectively. The dotted dashed line corresponds to a XDWBA calculation for the first $5/2^{+}$ resonance. The dotted line corresponds to an inert-core DWBA calculation where ground state and resonance are considered to be pure $s_{1/2}$ and $d_{5/2}$ states respectively. Experimental data are from Ref. [33].