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

TL;DR

The paper analyzes exclusive Z+1-jet production at 13 TeV to test jet-veto resummation in QCD. It reveals that ATLAS’s lepton-jet isolation inadvertently includes dijet events with a Z collinear to a jet, producing a giant $K$-factor that dominates high-$p_T^{\rm jet}$ and obscures resummation effects. By proposing an alternative isolation that vetoes collinear jet–lepton configurations, the authors show that jet-veto resummation becomes testable and that the $p_T^Z$ distribution serves as a robust complementary observable. The work motivates dual experimental measurements with both isolation criteria to isolate jet-veto physics and to validate resummation predictions relevant for Higgs analyses in the $WW$ final state.

Abstract

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.

Figures (7)

• Figure 1: Comparison of the resummed, matched and fixed order spectra (upper panel) and the relative deviations of the resummed and matched predictions with respect to the fixed-order result (lower panel) at 13 TeV for the ATLAS isolation criterion.
• Figure 2: Ratio of the correction factor $\Delta \sigma_{\text{non-global}}$ separated into initial-state partonic channels over the resummed cross section as a function of $p_T^{\rm jet}$.
• Figure 3: Ratio of the NLO fixed-order cross section over the LO result for 13 TeV for the ATLAS isolation criterion as well as the alternate isolation criterion.
• Figure 4: Comparison of the fixed-order NLO, resummed and matched results in 13 TeV for the alternate isolation criterion. The lower inset shows the relative deviations of the theoretical predictions with respect to fixed-order.
• Figure 5: Comparison of the leading double logarithms, single logarithms, and constant contributions to the exclusive cross section at relative order $\alpha_s$ with respect to the leading order. All the contributions are normalized to the LO cross section.