Neutron-neutron quasifree scattering in neutron-deuteron breakup

The neutron-deuteron (nd) breakup reaction provides a rich environment for testing models of the neutron-neutron (nn) interaction. Current theoretical predictions based on rigorous ab-initio calculations accurately describe most three-nucleon scattering data. One exception is the cross section for nn quasifree scattering (QFS) in nd breakup. Theoretical calculations underpredict recent measurements of the nn QFS cross section by more than 15%. This implies a large charge-symmetry breaking effect. We are conducting new measurements of the nn QFS cross section at the Triangle Universities Nuclear Laboratory.

The measurements are performed using two substantially different setups to assess systematic errors in the methods: the first uses shielded detectors with an open neutron source producing neutrons at 10 MeV and the second uses unshielded detectors with a collimated beam of 16 MeV neutrons. Time-of-flight techniques are used to determine the energies of the two neutrons detected in coincidence. A description of the experimental methods and preliminary results will be presented.