Precision Measurement Of The Neutron’s Beta Asymmetry Using Ultra‐Cold Neutrons Conference Paper uri icon


  • A measurement of Aβ, the correlation between the electron momentum and neutron (n) spin (the beta asymmetry) in n beta-decay, together with the n lifetime, provides a method for extracting fundamental parameters for the charged-current weak interaction of the nucleon. In particular when combined with decay measurements, one can extract the Vud element of the CKM matrix, a critical element in CKM unitarity tests. By using a new SD2 super-thermal source at LANSCE, large fluxes of UCN (ultra-cold neutrons) are expected for the UCNA project. These UCN will be 100% polarized using a 7 T magnetic field, and directed into the β spectrometer. This approach, together with an expected large reduction in backgrounds, will result in an order of magnitude reduction in the critical systematic corrections associated with current n β-asymmetry measurements. This paper will give an overview of the UCNA Aβ measurement as well as an update on the status of the experiment. © 2006 American Institute of Physics.

author list (cited authors)

  • Makela, M., Back, H. O., Melconian, D., & Plaster, B.

publication date

  • January 1, 2006 11:11 AM


  • AIP  Publisher