Release version 2.2.7

Sherpa 2.2.7

Version 2.2.7 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.

Download

The Sherpa package can be downloaded here: SHERPA-MC-2.2.7.tar.gz

In can also be accessed via git using

  • the web interface
  • or git clone -b rel-2-2-7 https://gitlab.com/sherpa-team/sherpa.git 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.

References

The main reference for Sherpa 2.2.x is arXiv:1905.09127. Please cite this publication if you have used Sherpa 2.2.x 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.

Examples

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.

Changelog

Known issues

  • Note that dijet production with additional jets merged with the CKKW algorithm is broken in the 2.2.x series (#46)
  • Also see our issue tracker

Enhancements

  • Add tools needed for the variable flavour number scheme in the multi-jet merging, cf. arXiv:1904.09382 (!146)
    • Add an option to cluster RS events in a fully ordered way (set COMIX_CLUSTER_RS_ORDERED=1)
    • Add a new scale scheme to the CS shower which should give better results for g->QQ splitting
    • Introduce a new scale tag P_TM2 defined as the root of the product of all transverse masses of all massive particles
  • Introduce new shower evolution schemes that take masses into account (set CSS_EVOLUTION_SCHEME=2 or 3) (!139)
  • Update default Lund string fragmentation parameters (!177)
  • Support the new analysis option feature in Rivet within the internal Rivet interface (!168)
  • Improve support for OpenLoops 2
  • Add an option to steer the total number of events generated in MPI event generation runs (!172)
  • Apply shower renormalisation scale factor to the strong coupling argument instead of re-defining AlphaS(mZ) (this improves the consistency of variations within Sherpa) (!145)
  • Add an option to switch on/off the multiple interaction library output (set MI_GENERATE_RESULTS_DIRECTORY=1 or 0) (!165)
  • Add an option to let the strong coupling value used in the shower freeze at a value of 1 instead of being cut off for low scales (this can mitigate cut-off issues when reweighting parton-shower emissions, cf. the manual) (!131)

Bugfixes (runtime issues)

  • Fix wrong eikonals in the top-decay showering (#176)
  • Fix issues in the CS shower emission reweighting (!131)
    • Fix max coupling setting for renormalisation scale reweighting
    • Fix reweightings below the accepted emission scale
    • Ignore reweightings if the target strong coupling value is zero (due to a different cut-off, this improves the statistics of the reweighted event sample)
  • Adjust hadron masses correctly when providing custom masses via MASS (!156)
  • Fix an issue with the VAR scale setter if its value was based asymmetrically on parton momenta (!141)
  • Fix broken IGNOREBEAMS switch for the internal Rivet interface (!148)
  • Use status code 11 for incoming particles with a strong charge for the HepMC_Short output format (this improves comptability with Rivet)

Bugfixes (compilation issues)

  • Replace C++ MPI bindings with C MPI bindings (C++ bindings were deprecated a long time ago and are not enabled per default in OpenMPI 4 (#77)