Measurement of the NP→PPπ− Reaction at 443 MEV

We measured the relative differential cross section and analyzing powers A SO, A NO and A LO for the reaction np→ppπ− at an incident neutron energy of 443 MeV. The geometry of our detector allowed us to sample almost all the available phase-space. We reconstructed the full kinematics of each event from the measured trajectories of at least two of the three final state particles. Cuts based on the vertex reconstruction and kinematic χ2 allowed us to remove most background, primarily nn→npπ− from the target walls and other materials. These cuts gave a signal-to-noise ratio of 22:1, but fewer than 3% of the total data survived the cuts. The resulting ~400,000 np→ppπ− were binned against p-p invariant mass and angles which are most suited to partial waves analysis. Comparisons are made to predictions of the model of Kloet and Lomon. These observables represent the first measurements of their kind at this energy and it is hoped that their determination will allow us to extract the role of isospin-0 amplitudes in the process of pion production.