DETERMINATIONS OF THE NEUTRON-NEUTRON SCATTERING LENGTH A(NN) FROM KINEMATICALLY INCOMPLETE NEUTRON-DEUTERON BREAKUP DATA REVISITED

We review published analyses of the final-state-interaction enhancemen t observed in proton energy distributions obtained from kinematically incomplete neutron-deuteron breakup experiments. We compare the result s derived from these analyses for the neutron-neutron scattering lengt h, a(nn), with our results based on a rigorous treatment of the three- nucleon Faddeev equations in conjunction with the use of realistic nuc leon-nucleon potentials. Our values for a(nn) deviate outside the quot ed uncertainties from the ones obtained in the previous analyses where simplified nucleon-nucleon interaction models were employed. In contr ast to the previous determinations, the present results for a(nn) are in clear disagreement with the values for a(nn) based on pi(-)-deutero n capture experiments. Unless inconsistencies in the experimental neut ron-deuteron breakup data at low energies can be resolved and the infl uence of possible three-nucleon-force effects can be reliably determin ed, we recommend that one not resort to the kinematically incomplete n eutron-deuteron breakup reaction as a tool for determining a quantity as important for nuclear and particle physics as is the neutron-neutro n scattering length a(nn).