Exploring core excitation in halo nuclei using halo effective field theory

Halo nuclei are exotic nuclear structures found far from stability near the dripline. Unlike stable nuclei, halo nuclei exhibit a large matter radius. This peculiar feature is the result of their strongly clusterised structure. They can be seen as a compact core to which one or two valence neutrons are loosely bound. Due to the quantum tunnel effect, they exhibit a high presence probability at a large distance from the other nucleons. Being located far from stability halo nuclei are mostly studied through reactions. To describe these reactions, it is essential to have reliable fewbody models of halo nuclei. This can be achieved by resorting to the halo effective field theory (Halo-EFT).

In this talk, I propose a simple structure model to account for that effect in the case of the typical one-neutron halo nucleus 11Be. I develop the Halo-EFT particle-rotor model to describe one-neutron halo nuclei, which takes core excitation into account. I solve the resulting equations, using the R-matrix method on a Lagrange mesh. Last, I study the impact of core excitation on the wave functions and scattering phaseshifts for the bound states of 11Be. In particular, I describe how to explicitly include the first 2+ excited state of the 10Be core in a few-body description of 11Be. I then compare my results with some high-precision ab initio calculations

For the 11Be's ground state, my results are in excellent agreement with the ab initio wave function and scattering phaseshift. This confirms the importance of core excitation in the description of this state and corroborates its halo structure. For 11Be's bound excited state, my model does not reproduce the ab initio predictions. This points to a state exhibiting a less clusterised structure.