Version 1.2.2 is an update of Sherpa which contains mainly bugfixes.

Sherpa 1.2.2

Version 1.2.2 is an update of Sherpa which contains mainly bugfixes. Please see the Changelog below for a summary of updates.

Download

The Sherpa package can be downloaded here:

A Manual is included in the Manual/ directory of the tarball. It is available in the HTML or INFO format and provides extensive documentation of all parameters. It can also be found online at http://projects.hepforge.org/sherpa/doc/SHERPA-MC-1.2.2.html.

A publication describing the physics of the SHERPA Monte-Carlo can be found in JHEP02 (2009) 007. This is meant to be the standard reference, please cite this publication if you have used SHERPA for your studies. Additionally each run will create a file called Sherpa_References.tex which contains information about the modules used in this run and the corresponding publications which should be referred.

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 briefly described in the manual.

We also provide a public gallery of results obtained with this version of Sherpa. There you can find comparisons to experimental data and to the previous version of Sherpa, as well as studies of systematics especially with respect to ME+PS merging.

A Changelog for important differences between the previous version and this version is provided below.

If you would like to be kept up-to-date about new versions or important updates of Sherpa, please subscribe to our announcement mailing list.

Patches/known problems/known bugs/FAQs

All known problems/questions and their solutions can be found on our issue tracker (please log in using the given details). If you encounter any problem while installing or running Sherpa, please open a new issue in the tracker. If your ticket has been closed and the problem is still unfixed, do not open a new ticket, but reopen the old one.

  • Bugfix for unweighted event generation using ME+PS merging, listed under ticket 98. Fix: Apply patch file via patch -p0 < unweighted_events.patch in the top level directory of your Sherpa installation, and recompile with make install.
  • There was a newly introduced bug for intermediate gravitons. Fix: Apply patch file via patch -p0 < add_propagator.patch in the top level directory of your Sherpa installation, and recompile with make install.
  • Bugfix to properly include radiation from multiple interactions in the HepEvt? output, listed under ticket 127. Fix: Apply patch file via patch -p0 < hepevt_interface.patch in the top level directory of your Sherpa installation, and recompile with make install.
  • Bugfix to preserve the graviton masses as generated by the MEs according to the ADD model, cf. ticket 126. Fix: Apply patch file via patch -p0 < add_masses.patch in the top level directory of your Sherpa installation, and recompile with make install.

Changelog

Bugfixes w.r.t. Version 1.2.1

  • Running couplings
    A problem in the treatment of interferences between graphs with different electroweak/QCD couplings has been solved, see ticket 69.
  • Photon ME+PS merging
    Photon-quark singularities were not always properly regularised in more complicated matrix elements by the ME+PS merging cut (thanks to Sandrine Laplace for helping in debugging this).
  • CS Shower kinematics
    The kinematics routines of the CSS are numerically more stable than in previous versions. Some minor bugs, affecting the showering in the presence of massive particles have been fixed, see ticket 60.
  • Default scale choice
    The kinematics routines of the default scale setter have improved simultaneously, see ticket 70. Also, a bug has been fixed, which only affected runs using AMEGIC with processes based on CSW vertex rules, see ticket 68.
  • Multithreaded integration with Comix
    A problem with multithreaded phasespace generation in Comix has been solved, see ticket 75.
  • Memory leak in hadronisation
    A memory leak has been removed in the interface between perturbative and non-perturbative event phases.
  • Spin correlations between AMEGIC++ and HADRONS++
    Spin correlations between tau leptons produced by AMEGIC++ in the hard process and their decays in the HADRONS++ module had been broken due to an interface change, see ticket 74.
  • Beam spectra
    Beam spectra like EPA did not work for process groups, i.e. processes involving particle containers like 93. This has been fixed, see ticket 67.
  • Cross Sections in Event Generation of pure QCD N>4 Multijet Events with MPI
    The inclusive cross section calculated during the generation of pure QCD multijet (N>4) events differend by a few percent depending on whether multi-parton interaction were switched on or off. This has been fixed, see ticket 90.
  • QED Radiation from ME in HepEvt? Output
    The matrix elmenent QED correction blob was not always properly translated into the HepEvt? output format. This has been fixed, see ticket 81.
  • Running Yukawa masses
    The running of Yukawa masses is now enabled by default, to make Higgs cross section calculations more meaningful. See ticket 79.
  • Parton separation criterion
    The interpretation of the value of the merging cut in the processes section has been revised such that it is more similar to the typical hardness as it would be defined by a kT criterion. In 1.2.1 the value was interpreted as twice that, i.e. the matrix element was used down to cuts half as low as intuitively expected.

New features/Improvements

  • Ordered clustering
    The parton shower history for truncated shower merging is now constructed in a maximally ordered way.
  • Alias particles in hadron decays
    It is now possible to define alias particles and their decay tables in the hadron decay module. This allows to define signal decay chains and was a request from LHCb. See ticket 59 for more information.
  • Relocatable installation
    The Sherpa installation can be made relocatable by specifying the --enable-binreloc configure option.
  • NTuple output for NLO Events
    A ROOT NTuple output method for matrix element level NLO event generation has been added. See the Manual for details.
  • Shortened HepMC2 Output
    A shortened HepMC2 output method containing only both beams and the final state stable hadrons has been added. See the Manual for details.