Measurement of the partial widths of the Z into up- and down-type quarks

Abstract Using the entire OPAL LEP1 on-peak Z hadronicdecay sample, Z → q q γ decays were selected by tagging hadronicfinal states with isolated photon candidates in the electromagnetic calorimeter. Combining the measured rates of Z → q q γ decays with the total rate of hadronicZ decays permits the simultaneous determination of the widths of the Z into up- and down-type quarks. The values obtained, with total errors, were Γ u =300 +19 −18 MeV and Γ d =381 +12 −12 MeV . The results are in good agreement with the Standard Model expectation.