Evidence of strong dynamic core excitation in C 19 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.