Matrix element method at NLO: A fine proof of concept in POWHEG
Abstract
The matrix element method (MEM) provides a fully probabilistic approach to confront experimental events with theory, retaining all correlations in the scattering matrix element. While leading-order MEM is widely used and automated, extending it to next-to-leading order (NLO) in QCD is challenging due to infrared divergences, negative weights, extra final-state partons, and multi-dimensional phase-space integration. We demonstrate that the POWHEG method offers a practical path to MEM at NLO accuracy. By projecting real-emission events onto Born kinematics via the mappings inherited from the B̃ (Φ) function, our method consistently includes the hardest QCD radiation while preserving the NLO-accurate normalization. As a proof of concept, we apply the method to fully leptonic W+W- production in the Standard Model effective field theory (SMEFT), considering a CP-even dimension-six triple-gauge-boson operator. At the parton level, the resulting NLO MEM exploits spin and polarization correlations in the final-state lepton kinematics, yielding enhanced discrimination between the SM and BSM hypotheses compared with conventional cut-and-count observables. Our results demonstrate the feasibility of incorporating NLO QCD corrections into the MEM and establish a framework for future applications to a broad range of collider processes.
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BibTeX
@misc{haisch2026matrix,
title = {{Matrix element method at NLO: A fine proof of concept in POWHEG}},
author = {Ulrich Haisch and Jakob Linder and Luc Schnell and Marius Wiesemann and Giulia Zanderighi},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.11083},
eprint = {2606.11083},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.11083},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Matrix element method at NLO: A fine proof of concept in POWHEG
AU - Ulrich Haisch
AU - Jakob Linder
AU - Luc Schnell
AU - Marius Wiesemann
AU - Giulia Zanderighi
PY - 2026
DA - 2026/10/12
PB - arXiv
DO - 10.48550/arxiv.2606.11083
UR - https://arxiv.org/abs/2606.11083
AB - The matrix element method (MEM) provides a fully probabilistic approach to confront experimental events with theory, retaining all correlations in the scattering matrix element. While leading-order MEM is widely used and automated, extending it to next-to-leading order (NLO) in QCD is challenging due to infrared divergences, negative weights, extra final-state partons, and multi-dimensional phase-space integration. We demonstrate that the POWHEG method offers a practical path to MEM at NLO accuracy. By projecting real-emission events onto Born kinematics via the mappings inherited from the B̃ (Φ) function, our method consistently includes the hardest QCD radiation while preserving the NLO-accurate normalization. As a proof of concept, we apply the method to fully leptonic W^+W^- production in the Standard Model effective field theory (SMEFT), considering a CP-even dimension-six triple-gauge-boson operator. At the parton level, the resulting NLO MEM exploits spin and polarization correlations in the final-state lepton kinematics, yielding enhanced discrimination between the SM and BSM hypotheses compared with conventional cut-and-count observables. Our results demonstrate the feasibility of incorporating NLO QCD corrections into the MEM and establish a framework for future applications to a broad range of collider processes.
ER -