Matrix element corrections in the Pythia8 parton shower in the context of matched simulations at next-to-leading order

Stefano Frixione; Simone Amoroso; Stephen Mrenna

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arXiv · 2308.06389

Matrix element corrections in the Pythia8 parton shower in the context of matched simulations at next-to-leading order

Stefano Frixione·Simone Amoroso·Stephen Mrenna

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Abstract

We discuss the role of matrix element corrections (MEC) to parton showers in the context of MC@NLO-type matchings for processes that feature unstable resonances, where MEC are liable to result in double-counting issues, and are thus generally not employed. By working with Pythia8, we show that disabling all MEC is actually unnecessary in computations based on the narrow-width approximation, and we propose alternative MEC settings which, while still avoiding double counting, allow one to include hard-recoil effects in the simulations of resonance decays. We illustrate our findings by considering top-antitop production at the LHC, and by comparing MadGraph_aMC@NLO predictions with those of POWHEG-BOX and standalone Pythia8.

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Stefano Frixione, Simone Amoroso, Stephen Mrenna. 2023-08-11. Matrix element corrections in the Pythia8 parton shower in the context of matched simulations at next-to-leading order. https://arxiv.org/abs/2308.06389

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