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Out-of-plane QCD radiation in hadronic Z0 production

We present the QCD analysis of the cumulative out-of-event-plane momentum distribution in the process proton-antiproton into Z0 and a hard jet (event plane defined by the proton, antiproton and Z0 momenta). Particular attention is placed on the near-to-planar events for which we derive the all-order resummed result to next-to-leading accuracy. We consider also the leading power correction originating from the fact that, even in hard processes, the resummed QCD coupling runs into the infrared region. We aim at the same level of accuracy which, in e+e- annihilation, seems to be sufficient for making predictions. Contributions from a ``soft underlying event'' due to beam remnant interactions are discussed. Experimental data (not yet available) are needed to cast light on the predictive level of standard QCD analysis in hard hadron-hadron collisions. We plot examples of the predicted distribution at Tevatron energies. The techniques here developed can be extended to other hard hadron-hadron and hadron-lepton processes.