Giant QCD K-factors beyond NLO

TL;DR

This paper introduces LoopSim, a method to approximate NNLO corrections for Z+jet processes at TeV scales, addressing large NLO K-factors and improving theoretical predictions for collider observables.

Contribution

The paper presents LoopSim, a novel unitarity-based approach to estimate approximate NNLO corrections for hadronic Z+jet observables, extending beyond existing NLO calculations.

Findings

LoopSim accurately reproduces known NNLO results for Drell-Yan spectra.

Approximate NNLO predictions show large K-factors in Z+jet observables.

Method provides insights into jet events even without giant K-factors.

Abstract

Hadronic observables in Z+jet events can be subject to large NLO corrections at TeV scales, with K-factors that even reach values of order 50 in some cases. We develop a method, LoopSim, by which approximate NNLO predictions can be obtained for such observables, supplementing NLO Z+jet and NLO Z+2-jet results with a unitarity-based approximation for missing higher loop terms. We first test the method against known NNLO results for Drell-Yan lepton pt spectra. We then show our approximate NNLO results for the Z+jet observables. Finally we examine whether the LoopSim method can provide useful information even in cases without giant K-factors, with results for observables in dijet events that can be compared to early LHC data.