Manifestation of the halo structure in momentum distributions from 6He fragmentation

Experimental data on the momentum distribution in the fragmentation of a 240 MeV/u He-6 beam on a carbon target are compared with several models of the He-6 nucleus based on different physical assumptions. It is shown that the lack of a strict theoretical description of the fragmentation mechanism and, in particular, of the final state interaction prevents any contra or versa arguments for these models. The requirement of fragment (He-5) survival or spatial localization of a fragment in the He-6 wave function is an essential point in the reaction mechanism. The analysis of the He-5 momentum (sum of the neutron and the alpha-particle momenta) distribution is free from the effect of final state interaction and thus more promising. It is shown that due to the requirement of fragment survival this distribution is determined mainly by the asymptotic of the He-6 wave function. Large sensitivity to the outer part of the halo structure gives a unique possibility to estimate the admixture of s-waves in the ground states of Li-11 and Be-14 directly from the momentum distribution of Li-10 (in fragmentation of Li-11) and from the momentum distribution of Be-13 (in fragmentation of Be-14). The shell structure of these nuclei is of great