The NPDGamma Experiment at LANSCE

The NPDGamma collaboration has constructed and commissioned an apparatus to determine the size of the pion-nucleon coupling constant in the parity non conserving pion exchange weak potential for N-N interactions. This coupling constant is directly proportional to the parity violating up-down asymmetry in the angular distribution of -rays with respect to the neutron spin direction in the capture of polarized cold neutrons on protons. The mea