Invariant mass spectrum and α-n correlation function studied in the fragmentation of 6He on a carbon target

Abstract

Momentum distributions and invariant mass spectra from the breakup of 6He ions with an energy of 240 MeV/u interacting with a carbon target have been studied. The data were used to extract information about the reaction mechanism which is influenced by the structure of 6He. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the 5He resonance. The shape of the ( α + n) two-body invariant mass spectrum is interpreted as mainly reflecting the 5He ground state which is a J π = 3 2 − resonance. However, no evidence for correlations between α particles and neutrons is observed in the momentum widths of the distributions. It is demonstrated that a combined analysis of the two-body invariant mass spectrum and an appropriate correlation function may be used to determine the properties of the intermediate resonance.