Determination of quark electroweak Couplings from direct photon production in hadronic Zdecays

Abstract

We report on a comparison of isolated hard photon production in hadronic Z decays with the predictions of a next-to-leading order matrix-element calculation. We constrain the quark electroweak couplings to the Z boson with a simultaneous fit to three direct photon distributions, and combine this result with an independent constraint from our measurement of the total hadronic width of the Z, obtaining c(u) = 0.92 +/- 0.22 and c(d) = 1.63 +/- 0.15 where c(u,d) = 4(g(V)2BAR + g(A)2BAR)u,d. Our results are consistent with standard model predictions.