Release version 2.2.4

Sherpa 2.2.4

Version 2.2.4 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:


In can also be accessed via git using

  • the web interface
  • or git clone -b rel-2-2-4 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

  • New default parameters for hadronisation model to improve heavy flavour production fractions and meson/baryon ratios (thanks to Andrii Verbytskyi).
  • Updates to Recola interface with some new parameter (names), please refer to the manual.
  • Make STRICT_METS the default scale setter to guarantee full scale setting accuracy for unweighted events.

New features

  • Availability of DIRE NLO parton shower (cf. arXiv:1705.00742). This is not (yet) the default shower, in particular not in NLO-merged configurations.
  • Higher numerical stability in parton shower kinematics (re)construction.
  • Add OVERWEIGHT_THRESHOLD allowing user to cap maximal weight during event generation (cf. manual).
  • Avoid spuriously large weights in NLO-merged samples due to instable PDF ratios.
  • Add interface for hadron-level selectors.
  • Add Max_N_TChannels option in Amegic.
  • Add possibility to identify partons which originate in the hard decay handler.
  • Restructure gzip support such that it can be switched off at runtime (USE_GZIP).
  • Enable on-the-fly reweighting for calculations with the Higgs (Interference) add-on for HIGGS_INTERERENCE_MODE 1, 2, 3 or 4.


  • Bugfix in NLO-matched parton shower emission for non-trivial colour structures like in V+2j@NLO. This fixes an eta asymmetry which was visible at the ~2% level in such samples.
  • BSM models through UFO: fix running coupling behaviour and treatment of exotic color octets.
  • Bugfix in random generator for Poisson distributions with large mean values.
  • Bugfixes for segfaults and compiler warnings with gcc 7.1.
  • Bugfix for colour assignment in clustering for loop-induced merged processes.
  • Bugfix for decay showering in conjunction with NLO+PS matching.