Version 1.2.1 is an update of Sherpa which contains many physics improvements and bugfixes.

Sherpa 1.2.1

Version 1.2.1 is an update of Sherpa which contains many physics improvements and bugfixes. Please see the Changelog below for a summary of updates.


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 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.

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

  • HepEvt? translation of QED_Radiation blobs corrected regarding ticket#81. Fix: Apply patch file via patch -p0 < issue_no81.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.


Bugfixes w.r.t. Version 1.2.0

  • Algebra Interpreter
    Unary minuses in expressions, partially ignored previously, are now properly taken into account.
  • Matrix Element - Parton Shower merging
    Certain colour correlations between final states previously not considered in the implementation of the jet criterion are properly accounted for.
  • Matrix Element - Parton Shower merging
    A problem with the cluster algorithm of AMEGIC++ has been solved that lead to parton shower errors, producing the message Missing colour partner.

New features/Improvements

  • Deep-inelastic scattering simulation
    Simulation of deep-inelastic lepton-nucleon scattering is now possible. A first application and an analysis of H1 data are described in detail in arXiv:0912.3715. The corresponding setup is contained in the online Manual.
  • ME+PS merging for prompt photon production
    Merging of photons produced in real emission matrix elements with photons produced in the interleaved QCD+QED shower cascade has been implemented. Further details and a comparison to LEP and Tevatron data has been published in Phys. Rev. D 81, 034026 (2010).
  • HZTool interface
    It is now possible to run HZTool analyses on top of Sherpa events directly from the Sherpa run card. See Tips and Tricks in the Manual.
  • Automatic setting of coupling information
    In collisions with hadronic initial states, the perturbative order and the reference value of the strong coupling are chosen according to the PDF. These settings are printed on-screen during the initialisation phase.
  • PDF interfaces
    The internal interfaces have been updated to handle CTEQ6.6m/a PDFs, including error sets. MSTW PDFs for different values of &#945;_s can also be used. The default PDF has been changed to cteq66.
  • Coupling scale in CSS
    The scale for evaluating strong couplings in the initial state shower evolution was changed to account for proper simulation of deep-inelastic scattering.
  • Kinematics in CSS
    The splitting kinematics in the parton shower simulation have changed according to arXiv:0912.3501 The previous choice can be enabled as an option to study parton shower systematics.
  • ME+PS backward clustering improved
    In the backward clustering step of the ME+PS merging algorithm we now take into account the shower weight for each potential branching history instead of simply choosing the most probable history.
  • Hadronisation tune
    The fragmentation parameters have been tuned by the Professor team.
  • UE tune
    Due to the new default PDFs, a new MPI tune became necessary. Using the new parameters 'SCALE_MIN=2.0745' and 'RESCALE_EXPONENT=0.22271' obtained using the Professor tool, we find good agreement with Tevatron underlying event data at 630, 1800 and 1960 GeV.
  • Les Houches interface for one-loop amplitudes updated to agree with official proposal in arXiv:1001.1307
  • ME Integrator added for weak boson+jets production processes with >=2 jets. For large numbers of jets this integrator is more efficient and simpler than the standard integrator used by AMEGIC++