Release version 2.2.5

Sherpa 2.2.5

Version 2.2.5 is a bugfix release in the Cho Oyu series and we encourage all users to update to this version.

If you spot any problem, please send us an email. If you would like to be informed about newer releases, please subscribe to our announcement mailing list.


The Sherpa package can be downloaded here: SHERPA-MC-2.2.5.tar.gz

In can also be accessed via git using

  • the web interface
  • or git clone -b rel-2-2-5 for a local clone.

A Manual is included in the Manual/ directory of the tarball (or the git-clone). It is available in the HTML and INFO format and provides extensive documentation of all parameters. It can also be found online.


The main reference describing the physics of Sherpa is JHEP02 (2009) 007. Please cite this publication if you have used Sherpa for your studies. Additionally, each run will produce a file called Sherpa_References.tex which contains information about the modules used in this run and the corresponding publications which should be referred. If in doubt, please seek the advice of the Sherpa authors.


You can find a large collection of example setups for using SHERPA in various different colliders/processes in the Examples/ directory of the tarball. They are also described in the manual.


Known issues

  • As all releases in the v2.2.x series, dijet production using the multi-jet merging algorithm is broken, see #46. This is fixed in the upcoming v3.0. If you can not wait for it, you can use a v2.1.x release.

Interface changes

  • Add preliminary support for HepMC3 (this interface is still being tested)

New features

  • Improve decay showering off top quarks
  • Improve single-top support and add examples and documentation for its production channels
  • Improve hadronisation and hadron decays for heavy flavour production
  • Introduce a user hook framework which allows users to easily implement event generation afterburners, see Examples/Userhook
  • Add settings to output ME-only on-the-fly variations (along with the full ones):
  • New cut-off for parton-shower reweighting:
    CSS_REWEIGHT_SCALE_CUTOFF=<pt_min>, default: 5 GeV^2
    this is more generally applicable than using a cut-off on the number of reweighted emissions
  • Improve support for on-the-fly variations of clustering steps (reweight each step locally instead of doing it globally)


  • Fix issue with the overweight treatment for negative weights
  • Add missing shower weight in some event outputs, e.g. when using OUTPUT HepMC...[]
  • Fix issue with the overweight threshold for on-the-fly variations
  • Fix issue with non-trivial beam spectra handling
  • Fix possible issues with electron-"PDF" initialization
  • Fix issue with the ISR-channel threshold for leptonic collider
  • Fix X/Y functions in METOOLS (this is relevant for hadron decays)
  • Fix crash in decay-channel sorting
  • Fix crash when using EVENT_TYPE=HadronDecay
  • Fix issue with CSS strong coupling values when using non-trivial scale factors
  • Fix issue with QSF variations for real emission calculations with COMIX
  • Fix crash when doing on-the-fly variations and invalid dipole kinematics occur
  • Fix issue in the interplay of the flux and the BIWeight for 1->n processes
  • Fix issue when using vertices with a vanishing coupling
  • Fix rare "invalid amplitude" crashes
  • Fix issues when adding limits for the number of t-channel propagators in matrix elements
  • Fix issue with checking PDF availability when enforcing jet vetoes
  • Fix several compilation issues