The Neutron as a Fundamental Physics Laboratory

P. R. Huffman, J. M. Adams, M. Arif, M. S. Dewey, T. R. Gentile, D. M. Gilliam, D. L. Jacobson, D. R. Rich, J. S. Nico, A. K. Thompson, and F. E. Wietfeldt

The neutron is an excellent laboratory for probing the weak nuclear force. Two classes of experiments are being performed at the NIST Center for Neutron Research to characterize the weak interaction through measurements of parity violation and neutron beta decay.

Studies of parity violation in the neutron-nucleon system provide a filter for isolating the weak interaction of composite hadrons. The strong interaction alters the hadronic weak interaction so it is not simply related to the elementary weak interaction. Measurements of parity violating observables can be used to extract the hadronic coupling constants, which when combined with meson-exchange potentials, provide us with a model of the weak nucleon-nucleon interaction.

Neutron beta decay probes the weak interaction at the quark level. From measurements of the neutron lifetime and asymmetry coefficients, the Standard Model vector and axial-vector weak force coupling constants gv and ga can be extracted. These two coupling constants completely characterize the weak interaction at the quark level. In addition, measurements in neutron beta decay provide the cleanest laboratory to observe the weak interaction in first generation quarks.

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