NPDGamma: A Measurement of the ParityViolating Directional y-Ray Asymmetry inPolarized Cold Neutron Capture on Hydrogen

摘要

The NPDGamma experiment aims to measure the correlation between the neutron spin and the direction of the emitted photon in neutron-proton capture at low momentum transfer. An up-down parity violating asymmetry from this process can be related to the strength of the hadronic weak interaction between nucleons.The first phase of the experiment was completed in 2006 at LANSCE. The methodology will be discussed and preliminary results will be presented. The next run will start in 2009 at the SNS at ORNL with many improvements that will yield a measurement with a projected statistical error of 1 x 10-8, 20% of the predicted value for the asymmetry. This will allow the determination of the long range π contribution in the weak interaction between nucleons.