Extraction of the 1S0 neutron-neutron scattering length from a kinematically-complete n-d breakup experiment at TUNL

The 1S0 neutron-neutron (nn) scattering length's currently accepted value (ann=-18.6±0.3 fm) is derived exclusively from two π--d capture-reaction experiments, in disagreement with the average -16.7±0.5 fm extracted from kinematically-complete nd breakup experiments. This discrepancy may be due to deficiencies in the analyses of n-d breakup data and/or three-nucleon force (3NF) effects. A kinematically-complete n+d→n1+n2+p breakup experiment at an incident neutron energy of 13.0 MeV was performed recently at TUNL. The value of ann was extracted from the direct comparison of experimental and rigorously-calculated theoretical nd breakup differential cross sections at four production angles of the nn pair. Using modern nucleon-nucleon potential models in the three-nucleon cross-section calculations we obtained ann=-18.7±0.6 fm, in agreement with the π--d result. We found no significant effect due to 3NFs on our ann value