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Herwig++ 2.3 Release Note

M. Bahr, S. Gieseke, M. Gigg, D. Grellscheid, K. Hamilton, S. Platzer, P. Richardson, M. H. Seymour, J. Tully

TL;DR

Herwig++ 2.3 extends the Monte Carlo event generator to cover lepton-hadron collisions, incorporates several NLO processes via the POWHEG scheme, and broadens BSM capabilities to include finite-width effects and three-body decays. It introduces a color-structure–based kinematic reconstruction, a new baryon-decay model with excited multiplets, and an enhanced underlying-event model featuring double parton scattering and a soft component. The release also adds new matrix elements for DIS and e+e- processes, refines the ThePEG interface for vertex structures, and includes a Contrib directory for external modules. Together, these updates deliver more realistic simulations for hadron-hadron and lepton-hadron environments, improved DIS/e+e- functionality, and a more flexible and tunable underlying-event description, positioning the project for continued evolution toward version 3.0.

Abstract

A new release of the Monte Carlo program Herwig++ (version 2.3) is now available. This version includes a number of improvements including: the extension of the program to lepton-hadron collisions; the inclusion of several processes accurate at next-to-leading order in the POsitive Weight Hardest Emission Generator (POWHEG) scheme; the inclusion of three-body decays and finite-width effects in Beyond the Standard Model (BSM) physics processes; a new procedure for reconstructing the kinematics of the parton shower based on the colour structure of the hard scattering process; a new model for baryon decays including excited baryon multiplets; the addition of a soft component to the multiple scattering model of the underlying event; new matrix elements for Deep Inelastic Scattering (DIS) and e+e- processes.

Herwig++ 2.3 Release Note

TL;DR

Herwig++ 2.3 extends the Monte Carlo event generator to cover lepton-hadron collisions, incorporates several NLO processes via the POWHEG scheme, and broadens BSM capabilities to include finite-width effects and three-body decays. It introduces a color-structure–based kinematic reconstruction, a new baryon-decay model with excited multiplets, and an enhanced underlying-event model featuring double parton scattering and a soft component. The release also adds new matrix elements for DIS and e+e- processes, refines the ThePEG interface for vertex structures, and includes a Contrib directory for external modules. Together, these updates deliver more realistic simulations for hadron-hadron and lepton-hadron environments, improved DIS/e+e- functionality, and a more flexible and tunable underlying-event description, positioning the project for continued evolution toward version 3.0.

Abstract

A new release of the Monte Carlo program Herwig++ (version 2.3) is now available. This version includes a number of improvements including: the extension of the program to lepton-hadron collisions; the inclusion of several processes accurate at next-to-leading order in the POsitive Weight Hardest Emission Generator (POWHEG) scheme; the inclusion of three-body decays and finite-width effects in Beyond the Standard Model (BSM) physics processes; a new procedure for reconstructing the kinematics of the parton shower based on the colour structure of the hard scattering process; a new model for baryon decays including excited baryon multiplets; the addition of a soft component to the multiple scattering model of the underlying event; new matrix elements for Deep Inelastic Scattering (DIS) and e+e- processes.

Paper Structure

This paper contains 13 sections, 2 figures.

Table of Contents

  1. Introduction
  2. Availability
  3. Lepton-Hadron Collisions and Kinematic Reconstruction
  4. Powheg
  5. BSM Physics
  6. New Matrix Elements
  7. Baryon Decays
  8. Underlying Event
  9. Double parton scattering
  10. Soft component
  11. Contrib
  12. Other Changes
  13. Summary

Figures (2)

  • Figure 1: Contour plots for the $\chi^2$ per degree of freedom of describing the transverse region from Affolder:2001xt. The cross indicates the location of our preferred tune and the white area consists of parameter choices where the elastic $t$-slope and the total cross section cannot be reproduced simultaneously.
  • Figure 2: Multiplicity and transverse momentum sum in the transverse region. CDF data are shown as black circles. The histograms show Herwig++ with the improved model for semi-hard and soft additional scatters using the MRST 2001 LO Martin:2001es PDFs for three different parameter sets. The lower plot shows the ratio Monte Carlo to data and the data error band. The legend on the upper plot shows the total $\chi^2$ for all observables.