CERN-PH-TH/2008-038 Cavendish-HEP-08/03 KA-TP-05-2008 DCPT/08/22 IPPP/08/11 CP3-08-05 Herwig++ Physics and Manual M. B¨ahr1, S. Gieseke1, M.A. Gigg2, D. Grellscheid2, K. Hamilton3, O. Latunde- Dada4, S. Pl¨atzer1, P. Richardson2, M.H. Seymour5,6, A. Sherstnev4, J. Tully2, B.R. Webber4 1 Institut f¨ur Theoretische Physik, Universit¨at Karlsruhe. 2 Department of Physics, Durham University. 3Centre for Particle Physics and Phenomenology, Universit´e Catholique de Louvain. 4 Cavendish Laboratory, University of Cambridge. 5 School of Physics and Astronomy, University of Manchester. 6 Physics Department, CERN. Authors’ E-mail:
[email protected] Abstract In this paper we describe Herwig++ version 2.3, a general-purpose Monte Carlo event generator for the simulation of hard lepton-lepton, lepton-hadron and hadron-hadron col- lisions. A number of important hard scattering processes are available, together with an interface via the Les Houches Accord to specialized matrix element generators for addi- tional processes. The simulation of Beyond the Standard Model (BSM) physics includes a range of models and allows new models to be added by encoding the Feynman rules of the model. The parton-shower approach is used to simulate initial- and final-state QCD radia- tion, including colour coherence effects, with special emphasis on the correct description of arXiv:0803.0883v3 [hep-ph] 2 Dec 2008 radiation from heavy particles. The underlying event is simulated using an eikonal multiple parton-parton scattering model. The formation of hadrons from the quarks and gluons produced in the parton shower is described using the cluster hadronization model.