HERWIG is a general-purpose Monte Carlo event generator, which includes the simulation of hard lepton-lepton, lepton-hadron and hadron-hadron scattering and soft hadron-hadron collisions in one package. It uses the parton-shower approach for initial-and final-state QCD radiation, including colour coherence effects and azimuthal correlations both within and between jets. This article updates the description of HERWIG published in 1992, emphasising the new features incorporated since then. These include, in particular, the matching of first-order matrix elements with parton showers, a more correct treatment of spin correlations and heavy quark decays, and a wide range of new processes, including many predicted by the Minimal Supersymmetric Standard Model, with the option of R-parity violation. At the same time we offer a brief review of the physics underlying HERWIG, together with details of the input and control parameters and the output data, to provide a self-contained guide for prospective users of the program. This version of the manual (version 3) is updated to HERWIG version 6.5, which is expected to be the last major release of Fortran HERWIG. Future developments will be implemented in a new C++ event generator, HERWIG++.The program is written in Fortran and the user has to modify the main program HWIGPR to generate the type and number of events required. See section 8.1 for a sample main program. The program operates by setting up parameters in common blocks and then calling a sequence of subroutines to generate an event. Parameters not set explicitly in the block data HWUDAT or in HWIGPR are set to default values in the main initialisation routine HWIGIN. Output data are delivered in the LEP standard common block HEPEVT [25,26]. Note that all real variables accessible to the user, including those in HEPEVT, are of type DOUBLE PRECISION.Since version 6.3, to take account of the increased energy and complexity of interactions at LHC and future colliders, the default value of the parameter NMXHEP, which sets the array sizes in the standard /HEPEVT/ common block, has been increased to 4000.To generate events the user must first set up the beam particle names PART1, PART2 (type CHARACTER*8) and momenta PBEAM1, PBEAM2 (in GeV/c), a process code IPROC and the number of events required MAXEV.See section 4 for beams and processes available. All analysis of generated events (histogramming, etc.) should be performed by the user-provided routines HWABEG (to initialise the run), HWANAL (to analyse an event) and HWAEND (to terminate the run).A detailed event summary is printed out for the first MAXPR events (default MAXPR = 1). Setting IPRINT = 2 lists the particle identity codes, properties and decay schemes used in the program.The programming language is standard Fortran 77 as far as possible. However, the following may require modification for running on some computers • Most common blocks are inserted by INCLUDE 'HERWIG65.INC' statementsthe file HERWIG65.INC is part of the standard program package.• Many common blo...

Abstract:We describe the implementation of supersymmetric processes in the HERWIG Monte Carlo event generator. We define relevant parameter and mixing conventions and list the hard scattering matrix elements. Our implementation is based on the Minimum Supersymmetric Standard Model, with the option of R-parity violation. The sparticle spectrum is completely general. Both hadron-hadron and lepton-lepton collisions are covered. This article supplements a separate publication in which the general features of HERWIG 6.2 are described, and updates the treatment of supersymmetry to version 6.4.

A spectrum of massive graviton states is present in several recent theoretical models that include extra space dimensions. In some such models the graviton states are well separated in mass, and can be detected as resonances in collider experiments. The ability of the ATLAS detector at the Large Hadron Collider to identify such states and measure their properties is considered, in the case that the resonances are narrow compared to the experimental resolution. The discovery limits for the detection of the decay mode G → e + e − are derived. The angular distribution of the lepton pair is used to determine the spin of the intermediate state. In one specific model, the resonance can be detected up to a graviton resonance mass of 2080 GeV, while the angular distribution favours a spin-2 hypothesis over a spin-1 hypothesis at 90% confidence for resonance masses up to 1720 GeV.

Many models that include small extra space dimensions predict graviton states which are well separated in mass, and which can be detected as resonances in collider experiments. It has been shown that the ATLAS detector at the Large Hadron Collider can identify such narrow states up to a mass of 2080 GeV in the decay mode G → e + e − , using a conservative model. This work extends the study of the e + e − channel over the full accessible parameter space, and shows that the reach could extend as high as 3.5 TeV. It then discusses ways in which the expected universal coupling of the resonance can be confirmed using other decay modes. In particular, the mode G → γγ is shown to be measurable with good precision, which would provide powerful confirmation of the graviton hypothesis. The decays G → µ + µ − , W + W − , Z 0 Z 0 and jet-jet are measurable over a more limited range of couplings and masses. Using information from mass and cross-section measurements, the underlying parameters can be extracted. In one test model, the size of the extra dimension can be determined to a precision in length of 7 × 10 −33 m.

We study integrated and differential rates for the production of charged Higgs bosons H Ϯ of the minimal supersymmetric standard model via b-quark-initiated subprocesses in pp collisions at the CERN Large Hadron Collider. In detail, we compute cross sections and distributions of the reactions bU→bDH ϩ →bD ϩ c.c. and bU→bDH ϩ →bDtb→bDbbjj c.c., for a H Ϯ scalar in the intermediate ͑i.e., M Ϯ Ͻm t ϩm b ) and heavy ͑i.e., M Ϯ Ͼm t ϩm b ) mass range, respectively (U and D represent generic u-and d-type light quarks͒. In the former case, charged Higgs boson masses up to about 145 GeV can be covered for both large and small tan␤'s. In the latter case, charged scalars can be detected for values of M H Ϯ up to about 500 GeV, especially if tan␤ is large, and provided that either excellent b-tagging performances can be achieved or the high luminosity option becomes available. ͓S0556-2821͑97͒01009-6͔