GoSam is hosted by Hepforge, IPPP Durham

On this webpage you can find a collection of process packages for the simulation of selected hadron collider hard processes at next-to-leading order accuracy in QCD. The virtual parts have been created using GoSam
[G. Cullen, N. Greiner, G. Heinrich, G. Luisoni, P. Mastrolia, G. Ossola, T. Reiter and F. Tramontano; Eur.Phys.J. C72 (2012) 1889; arXiv:1111.2034]
, and interfaced to the Sherpa event generator through the Binoth-Les-Houches-Accord interface
[T. Binoth et al.; Comput.Phys.Commun. 181 (2010) 1612-1622; Conference: C09-06-08.1, p.1-19; arXiv:1001.1307]
. The packages run with Sherpa using the tree-level matrix elements
[F. Krauss, R. Kuhn, G. Soff; JHEP 0202 (2002) 044; arXiv: hep-ph/0109036.]
for the Born and the real corrections, the subtraction terms
[T. Gleisberg, F. Krauss; Eur.Phys.J. C53 (2008) 501-523; arXiv:0709.2881.]
following the Catani-Seymour
[S. Catani, M. Seymour; Nucl.Phys. B485 (1997) 291-419, Erratum-ibid. B510 (1998) 503-504; arXiv: hep-ph/9605323.]
and Catani-Dittmaier-Seymour-Trocsanyi
[S. Catani, S. Dittmaier, M. Seymour, Z. Trocsanyi; Nucl.Phys. B627 (2002) 189-265; arXiv: hep-ph/0201036]
schemes, a matching-procedure with a parton-shower
[S. Hoeche, F. Krauss, M. Schonherr, F. Siegert; Submitted to: Physical Review Letters; arXiv:1201.5882]
and the framework for the phase-space integration and analysis.

The gosamsherpa command-line script:

Provided you have the full GoSam package installed (details about the installation of GoSam can be found here) and Sherpa-1.4.X together with the GoSam patch (essential details about the installation of Sherpa with the patch are given below), the gosamsherpa command-line script allows to generate a code for the calculation of cross sections at NLO in the strong coupling constant. Executing

./gosamsherpa MySherpaFile.dat

will generate and install a code for the computation of the full QCD NLO corrections to the Standard Model process specified in the Sherpa card MySherpaFile.dat.

At the moment the script works only for processes without massive gauge-bosons in the loop and without production of resonant massive top-quarks. Below a collection of pre-generated GoSam-Sherpa packages for some selected processes is available. The packages already contain the GoSam virtual code and to run them the full installation of GoSam is not required.

Installation of pre-generated GoSam-Sherpa packages:

Important

DEPENDENCIES

To run the process packages you need the following:

  1. To run the packages Sherpa-1.4.1 (Sherpa 1.4.0 or 1.4.2 is also compatible provided you use the appropriate patch) must be installed. After downloading and unpacking Sherpa, run the GoSam patch (linux, mac) in the main Sherpa folder (usually called SHERPA-1.4.X) using:

    patch -p0 < linux_gosamsherpa-1.4.X.patch  OR  patch -p0 < mac_gosamsherpa-1.4.X.patch

    After the patch is successfully applied, configure, compile and install Sherpa normally with the following options enabled:

    --enable-lhole --enable-analysis

    The packages have been tested with the following further configurations enabled, which are however optional and need an already working installation of the relative packages (LHAPDF, Rivet, FastJet):

    --enable-lhapdf=path-to-lhapdf --enable-rivet=path-to-rivet --enable-fastjet=path-to-fastjet

    A parallel grid computation can be performed enabling the open-mpi option in Sherpa with

     --enable-mpi

    For details about the installation and usage of Sherpa we refer to the Sherpa online documentation.

  2. The fortran90 libraries for the virtual part in each process-package has been generated with GoSam. To run the packages the suite of programs gosam-contrib must be installed. The suite provides programs for the reduction and numerical evaluation of tensor and scalar loop integrals (avh-olo, golem95, qcdloop, samurai).

    Two options are available for this. Each package is available with and without the gosam-contrib suite included. The packages labelled with Stand-alone contain the gosam-contrib suite which is installed locally along with the virtual process. If you decide to use these one, you can skip the installation of the gosam-contrib and directly go to the next step.

    If instead you don’t want to have a version of the gosam-contrib suite for every single process-package you can install it only once in your system. To install the gosam-contrib suite unpack the tar.gz file and run

    ./configure --prefix=/desired/installation/path/to/gosam-contrib-1.0
    make
    make install

    where /installation/path/to/gosam-contrib-1.0 corresponds to the desired installation location, which we strongly recommend to set. Lastly, if the installation path of gosam-contrib is different from the default, do not forget to update the environment variable $LD_LIBRARY_PATH by doing the following in the .bashrc file:

    export LD_LIBRARY_PATH=/installation/path/to/gosam-contrib-1.0/lib:$LD_LIBRARY_PATH

    or alternatively, in the .cshrc file:

    setenv LD_LIBRARY_PATH ($LD_LIBRARY_PATH):/installation/path/to/gosam-contrib-1.0/lib

    A guide for the installation of the gosam-contrib suite from the svn repository che be found on the gosam installation page.

  3. To install and run the packages unpack the tarball and execute:

    ./makecode install

    After the script has finished, run

    Sherpa -f Run_LO.dat

    to get leading order prediction or, to get next-to-leading order prediction

    Sherpa -f Run_NLO.dat

    Plots can be produced (through gnuplot) executing

    ./makeplots

    For more details we refer to the README file contained in each tarball.

Process List: