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

13 pags, 5 figures.-- PACS nrs.: 24.60.−t; 25.70.Ef; 27.20.+n.Momentum distributions and invariant mass spectra from the breakup of He-6 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 He-6. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the He-5 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 cu 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.This work was supported by the German Federal Minister for Education and Research (BMBF) under Contracts 06 DA 820, 06 OF 474 and 06 MZ 476 and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts DARIK, OF ELK, MZ KRK and partly supported by the Polish Committee of Scientific Research under Contract PB2/P03B/113/09, EC under Contract ERBCHGE-CT92-0003 and CICYT under Contract AEN92-0788-C02-02 (MJGB) and by Deutsche Forschungsgemeinschaft (DFG) under Contract 436 RUS 130/127/1. One of us (B.J.)acknowledges the support through an Alexander von Humboldt Research Award.Peer reviewe