Combining Higher-Order Resummation with Multiple NLO Calculations and Parton Showers in GENEVA

TL;DR

This paper introduces a novel method combining higher-order resummation with NLO calculations and parton showers, achieving improved accuracy across jet resolutions in GENEVA for e+e and pp collisions.

Contribution

It develops a comprehensive approach that merges resummation and NLO matrix elements, enabling smooth transitions between different jet multiplicities and resolutions.

Findings

Good agreement with LEP data for 2-jet observables

Successful implementation in GENEVA framework with N-jettiness

Enhanced accuracy at small and large jet resolutions

Abstract

We extend the lowest-order matching of tree-level matrix elements with parton showers to give a complete description at the next higher perturbative accuracy in alpha_s at both small and large jet resolutions, which has not been achieved so far. This requires the combination of the higher-order resummation of large Sudakov logarithms at small values of the jet resolution variable with the full next-to-leading order (NLO) matrix-element corrections at large values. As a by-product this combination naturally leads to a smooth connection of the NLO calculations for different jet multiplicities. In this paper, we focus on the general construction of our method and discuss its application to e+e and pp collisions. We present first results of the implementation in the GENEVA Monte Carlo framework, where we employ N-jettiness as the jet resolution variable, combining its next-to-next-to-leading logarithmic resummation with fully exclusive NLO matrix elements, and PYTHIA8 as the backend for further parton showering and hadronization. For hadronic collisions, we take Drell-Yan production as an example to apply our construction. For e+e- -> jets, taking alpha_s(mZ) = 0.1135 from fits to LEP thrust data, together with the PYTHIA8 hadronization model, we obtain good agreement with LEP data for a variety of 2-jet observables.