Excitation Halo States of ¹²B

Angular distributions for the ¹¹B(d,p ¹²B transfer reactions have been measured at E_lab = 11.8 MeV. The asymptotic normalization coefficients (ANC) of the ground state, the second and third excitation states for ¹²B(¹¹B+n) are extracted from the differential cross sections at three forward angles. With these ANCs, the root-mean-square radii are calculated for these three states. The results show that the second and third excitation states of ¹²B are neutron halo states.