Studies of strong and electroweak interactions using final state photon emission in hadronicZ 0 decays

The cross section and jet rates ofZ0 decays into photons and quarks are compared with matrix element Monte Carlos ofO(ααs). Good agreement is found between data and theoretical predictions. From the ratio of events with three jets plus a photon to those with two jets plus a photon, αs in first order is determined to be 0.176±0.010. Combining the cross section of final state photon events with the LEP average hadronic partial decay width of theZ0, the widths of theZ0 into up and down type quarks can be calculated. The results $$\begin{gathered} \Gamma _{u - type} = 242 \pm 46MeV; \hfill \\ \Gamma _{d - type} = 419 \pm 30MeV \hfill \\ \end{gathered} $$ are in good agreement with the standard model expectation. A comparison of the measured cross section as a function ofycut with predictions of QCD shower models shows that, at the current level of accuracy ARIADNE and, to a lesser extent, HERWIG and JETSET can reproduce the measurement.