NPDGamma is an ongoing effort to measure the parity-violating asymmetry in polarized cold neutron capture on parahydrogen.

Polarized neutrons of energies 2meV – 15meV are incident on a liquid parahydrogen target. The neutrons are captured, forming deuterium and releasing a gamma ray with an energy of 2.2MeV (the binding energy of deuterium), which is subsequently detected. The detector array consists of 4 rings of 12 detectors each, where each ring is concentric around the neutron beam. The polarization of the incoming neutron beam is alternated rapidly to study the spin correlation of the direction of the emitted gamma ray.

), the long-range coupling constant used to describe the hadronic weak interaction.

The first phase of the NPDGamma experiment was carried out at Los Alamos National Lab).

The current phase of the NPDGamma experiment is running at the Spallation Neutron Source at Oak Ridge National Lab. Production data began in the spring of 2012.

In 2018 the NPDGamma collaboration reported a successful measurement of parity violation.

References

External links

• Experiment Wiki