Out-of-plane QCD radiation in hadronic Z0 production

TL;DR

This work develops a comprehensive QCD framework for the cumulative out-of-event-plane momentum $K_{\rm out}$ in hadronic Z0 production with an associated hard jet. It performs all-order resummation to next-to-leading accuracy, factorizes incoming-state evolution from the radiation factor, and incorporates leading non-perturbative corrections via a dispersive approach and the Milan factor. The methodology yields a perturbative distribution, its fixed-order matched extension, and a leading NP shift, with numerical illustrations for Tevatron kinematics and explicit discussion of beam-remnant underlying-event effects. The analysis provides a structured template to study radiation in hard hadron-hadron collisions and can be extended to other processes, offering a baseline to test standard QCD against potential non-hard contributions.

Abstract

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.