Abstract
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 α 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. 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 Pythia 8 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 α s (m Z) = 0.1135 from fits to LEP thrust data, together with the Pythia 8 hadronization model, we obtain good agreement with LEP data for a variety of 2-jet observables.
Highlights
Accurate and reliable theoretical predictions for measurements at collider experiments require the inclusion of QCD effects beyond the lowest perturbative accuracy in the strong coupling αs
We extend the lowest-order matching of tree-level matrix elements with parton showers to give a complete description at the higher perturbative accuracy in αs at both small and large jet resolutions, which has not been achieved so far
In the end, providing an accurate description of this transition region requires a careful combination of both types of corrections. Such a Monte Carlo description at relative O(αs) accuracy across phase space has never been achieved and is the subject of our paper. (We briefly summarize the existing efforts to combine NLO corrections with parton showers in section 1.1 below.) The crucial starting point in our approach is that all perturbative inputs to the Monte Carlo are formulated in terms of well-defined physical jet cross sections [3, 4]
Summary
Accurate and reliable theoretical predictions for measurements at collider experiments require the inclusion of QCD effects beyond the lowest perturbative accuracy in the strong coupling αs. In the end, providing an accurate description of this transition region requires a careful combination of both types of corrections Such a Monte Carlo description at relative O(αs) accuracy across phase space has never been achieved and is the subject of our paper. (We briefly summarize the existing efforts to combine NLO corrections with parton showers in section 1.1 below.) The crucial starting point in our approach is that all perturbative inputs to the Monte Carlo are formulated in terms of well-defined physical jet cross sections [3, 4] This allows us to systematically increase the perturbative accuracy by incorporating results for the relevant ingredients to the desired order in fixed-order and resummed perturbation theory.
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