Extraction of the [sup 1]S[sub 0] neutron-neutron scattering length from a kinematically-complete n-d breakup experiment at TUNL

The [sup 1]S[sub 0] neutron-neutron ([ital nn]) scattering length[close quote]s currently accepted value (a[sub nn]=[minus]18.6[plus minus]0.3 hthinsp;fm) is derived exclusively from two [pi][sup [minus]]-d capture-reaction experiments, in disagreement with the average [minus]16.7[plus minus]0.5 hthinsp;fm extracted from kinematically-complete [ital nd] breakup experiments. This discrepancy may be due to deficiencies in the analyses of n[minus]d breakup data and/or three-nucleon force (3NF) effects. A kinematically-complete n+d[r arrow]n[sub 1]+n[sub 2]+p breakup experiment at an incident neutron energy of 13.0 MeV was performed recently at TUNL. The value of a[sub nn] was extracted from the direct comparison of experimental and rigorously-calculated theoretical [ital nd] breakup differential cross sections at four production angles of the [ital nn] pair. Using modern nucleon-nucleon potential models in the three-nucleon cross-section calculations we obtained a[sub nn]=[minus]18.7[plus minus]0.6 hthinsp;fm, in agreement with the [pi][sup [minus]]-d result. We found no significant effect due to 3NFs on our a[sub nn] value. [copyright] [ital 1999 American Institute of Physics.]