Is the Unitarity of the Quark-Mixing CKM Matrix Violated in Neutronβ-Decay?

We report on a new measurement of neutron β-decay asymmetry. From the result A₀0ex0ex=0ex0ex-0.1189(7), we derive the ratio of the axial vector to the vector coupling constant λ0ex0ex=0ex0exgA/gV0ex0ex=0ex0ex-1.2739(19). When included in the world average for the neutron lifetime τ0ex0ex=0ex0ex885.7(7)0ex0exs, 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 Δ0ex0ex=0ex0ex0.0083(28), which is 3.0 times the stated error.