Jet vetoes versus giant K-factors in the exclusive Z+1-jet cross section

We perform a detailed study of the exclusive Z+1-jet cross section at the 13 TeV LHC, motivated by the importance of similar exclusive cross sections in understanding the production of the Higgs boson in the W^+W^- final state. We point out a feature of the ATLAS analysis that has significant impact on the theoretical predictions: the jet-isolation criterion implemented by ATLAS effectively allows dijet events where an energetic jet is collinear to a final-state lepton. This process contains a giant $K$-factor arising from the collinear emission of a Z-boson from the dijet configuration. This overwhelms the effect of the jet-veto logarithms, making it difficult to test their resummation in this process. We provide numerical results that demonstrate the interplay between the jet-veto logarithms and the giant K-factor in the theoretical prediction. We study several observables, including the transverse momentum distributions of the leading jet and the Z-boson, in the exclusive Z+1-jet process, and discuss their sensitivity to both the giant K-factor and the jet-veto logarithms. We suggest a modified isolation criterion that removes the giant K-factor and allows for a direct test of the jet-veto resummation framework in the exclusive Z+1-jet process.