Degree to which CVC is Established Through Beta Decay Alone
  Precision studies of $0^{+} \rightarrow 0^{+}$ superallowed $\beta$ decays provide the necessary data to test stringently the CVC hypothesis. They will also provide a value for the weak vector coupling constant and the $V_{ud}$ quark mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. The determination of this element is crucial for the test of the unitarity of the CKM matrix, and the search for physics beyond the Standard Model. This paper reviews the current status of $0^{+} \rightarrow 0^{+}$ $\beta$-decay data and their implications, as well as some relevant data from the $\beta$ decay of $^{19}$Ne and the neutron. 
E. Hagberg, J.C. Hardy, V.T. Koslowsky, G. Savard and I.S. Towner   (Chalk River Laboratories)