Is the Unitarity of the quark-mixing-CKM-matrix violated in neutron β-decay?
Abstract
We report on a new measurement of neutron β-decay asymmetry. From the result A0 = -0.1189(7), we derive the ratio of the axial vector to the vector coupling constant λ = gA/gV = -1.2739(19). When included in the world average for the neutron lifetime τ = 885.7(7)s, this gives the first element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix Vud . With this value and the Particle Data Group values for Vus and Vub, we find a deviation from the unitarity condition for the first row of the CKM matrix of = 0.0083(28), which is 3.0 times the stated error.
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