Experimental Evidence for Electroweak Corrections Beyond Fermion Loops

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We reemphasize the importance of discriminating fermion-loop and bosonic electroweak corrections in the analysis of electroweak precision data. Most recent data are indeed precise enough to require corrections beyond (trivial) fermion loops. An analysis of these data in terms of the observables Δx ≡ εₙ₁ - εₙ₂, Δy ≡ - εₙ₂ and ε≡ - εₙ₃ identifies the required additional corrections as vertex corrections at the W± f f′ and Z⁰ f f vertices. Standard-model values for these corrections are consistent with the experimental data.