Probing the quadrupole transition strength of ¹⁵C by deuteron inelastic scattering

Valence-neutron decoupling is expected to happen in one-neutron halo nuclei due to the extended wave function of the valence neutron. The degree of coupling can be described by the difference in the neutron and proton contribution to the quadrupole transition. Core polarization in the transition between the ground state and first excited state in one-neutron halo nucleus ¹⁵C might be weakly induced by the valence neutron. In order to investigate it, deuteron elastic scattering from ¹⁵C and inelastic scattering reactions to the first excited state of ¹⁵C were measured using a radioactive beam of ¹⁵C in inverse kinematics using HELIOS. The matter deformation length δ_d=1.04(10) fm has been extracted from the inelastic scattering differential cross sections. The ratio of neutron and proton matrix element M_n/M_p=3.56(36) has been determined. Neutron and proton effective charges of ¹⁵C will be discussed. Results from ab-initio no-core configuration interaction calculations will also be compared with the experimental observations. This result supports a moderated core decoupling effect of the valence neutron in ¹⁵C, in line with the interpretation of other carbon isotopes.