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arXiv · 2512.16645

The Physics of Herwig 7

J. Bellm·G. Bewick·S. Ferrario Ravasio·S. Gieseke·D. Grellscheid·S. Kiebacher·P. Kirchgaeßer·F. Loshaj·M. R. Masouminia·G. Nail·A. Papaefstathiou·S. Plätzer·M. Rauch·P. Reimitz·C. Reuschle·P. Richardson·D. Samitz·P. Sarmah·P. Schichtel·M. H. Seymour·A. Siódmok·D. Stafford·C. B. Strange·S. Sule·S. Webster·J. Whitehead
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Abstract

We present the physics foundations and recent developments of Herwig 7, the modern successor of the original HERWIG and Herwig++ series. Herwig 7 provides a flexible and systematically improvable framework for the simulation of high-energy lepton and hadron collisions, with particular emphasis on QCD and EW effects. Hard scattering processes are generated within the automated Matchbox framework, which integrates external amplitude providers, supports tree-level, next-to-leading-order (NLO) and loop-induced matrix elements, and implements subtraction schemes, multi-channel phase-space sampling, dynamic scale choices and both POWHEG- and MC@NLO-type matching algorithms. Consistent multijet merging at LO and NLO is provided, enabling precise predictions across a wide range of SM processes. Parton radiation is simulated using two complementary showers: an angular-ordered shower incorporating QCD coherence and the heavy-quark dead-cone effect, and a dipole shower optimised for NLO matching and multijet merging. Higher-order corrections are included through matrix-element corrections and dedicated reweighting techniques, while QED and EW radiation are treated using a YFS formalism and EW showering algorithms. The modelling of non-perturbative physics employs an advanced cluster hadronization framework with improved cluster formation, fission and decay, as well as colour reconnection models, heavy-quark effects and interfaces to alternative hadronization schemes. An extended eikonal multiple-partonic-scattering model, incorporating semi-hard and soft components together with diffractive interactions, enables realistic descriptions of minimum-bias and underlying-event data. Herwig 7 thus represents a versatile event generator, providing a coherent, modular and extensible platform for Standard Model and beyond-the-Standard-Model collider phenomenology at current and future facilities.

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J. Bellm, G. Bewick, S. Ferrario Ravasio, S. Gieseke, D. Grellscheid, S. Kiebacher, P. Kirchgaeßer, F. Loshaj, M. R. Masouminia, G. Nail, A. Papaefstathiou, S. Plätzer, M. Rauch, P. Reimitz, C. Reuschle, P. Richardson, D. Samitz, P. Sarmah, P. Schichtel, M. H. Seymour, A. Siódmok, D. Stafford, C. B. Strange, S. Sule, S. Webster, J. Whitehead. 2025-12-18. The Physics of Herwig 7. https://arxiv.org/abs/2512.16645

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