Description: We measure the correlation between the neutron spin and the momentum of the electrons emitted following beta-decay (the beta-asymmetry) utilizing, for the first time, ultra-cold neutrons (UCN).
This angular correlation is a function of the fundamental semi-leptonic form factors for the nucleonic charged weak current. Our measurements provide a direct determination of the axial coupling constant of the nucleon, gA.Taken together with the lifetime of the neutron and the muon, they provide a nuclear-structure independent extraction of the CKM matrix element Vud.
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