Coulomb Breakup Mechanism of Neutron-Halo Nuclei in a Time-Dependent Method

The mechanism of the Coulomb breakup reactions of the nuclei with neutron-halo structure is investigated in detail. A time-dependent Schr\"odinger equation for the halo neutron is numerically solved by treating the Coulomb field of a target as an external field. The momentum distribution and the post-acceleration effect of the final fragments are discussed in a fully quantum mechanical way to clarify the limitation of the intuitive picture based on the classical mechanics. The theory is applied to the Coulomb breakup reaction of $^{11}$Be + $^{208}$Pb. The breakup mechanism is found to be different between the channels of $j^{\pi}=\frac{1}{2}^{-}$ and $\frac{3}{2}^{-}$, reflecting the underlying structure of $^{11}$Be. The calculated result reproduces the energy spectrum of the breakup fragments reasonably well, but explains only about a half of the observed longitudinal momentum difference.