charybdis 2 - dependencies

Dependencies

As provided in the Downloads section, CHARYBDIS2 can run in 3 different modes. Here we explain each of the 3 modes briefly. This section complements the step by step instructions in Downloads.

You can find an example mainprogram for each mode, but some libraries may need to be installed, or source code files will need to be downloaded and edited, for interfacing with herwig or pythia. In what follows a summary of the libraries that each implementation depends on is given. For more details please refer to the Manual.

The implementation you choose, must be set in the Makefile by giving one of the following 3 values to the flag GENERATOR:

CHARYBDIS (parton level mode): Only parton level events are generated using the proton pdfs together with the parton level production cross section. Then the decay/evaporation is performed to obtain the final state particles. This mode requires the use of an external pdf library. Therefore you will need one of the libraries installed:

LHAPDF - which you can find on the LHAPDF website.
PDFLIB - this is part of CERNLIB.

In the Makefile you will have to set the flag PDFCHOICE (either to LHAPDF or PDFLIB) and provide the path to your installation directory of the pdf library by setting LPDF (see examples in the Makefile provided).

In both remaining implementations the parton level hard process is generated as in the parton level mode and then interfaced to Herwig or Pythia for parton showering, secondary decays and hadronisation. The interfacing is done through the Les Houches accord.
In both cases you will have to delete the dummy Les Houches subroutines UPINIT and UPEVNT and the dummy PDFLIB subroutines PDFSET and STRUCTM from the HERWIG or PYTHIA source code files (these routines are redefined in the charybdis2-*.*.*.F source code file).

HERWIG : This implementation can be set to use PDFLIB or HERWIG's internal pdfs. PDFCHOICE must be set either to the value PDFLIB or left blank respectively. Note that LHAPDF is not allowed!
In addition, the herwig source code filename must be specified by setting HERWIGSRC = src_filename.f. CHARYBDIS2 has been tested extensively with the last version of HERWIG (6.510) which is the recomended one. However earlier Les Houches accord compliant versions may still run, but some functionalities specific to CHARYBDIS2 may be lost. You can find information and the source code for HERWIG here.
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PYTHIA : The pdf choices are as for HERWIG (PDFLIB or internal pdfs). You will need a Les Houches compliant version of PYTHIA which means any version above 6.220. The pythia source code filename must be specified by setting PYTHIASRC = src_filename.f. You can find information and the source code for pythia here.
Note: Even though the polarisation information of the final state particles is kept in the Les Houches common blocks when the CHARYBDIS2 hard process is called, PYTHIA does not use this information! So if you are interested in polarisation effects you will either have to use the HERWIG implementation, or generate Les Hoches event files. For the latter, you can then feed the Les Houches file inot another general purpose event generator that uses the polarisation information (for more information on how to produce Les Houches event files please look into the Manual. Note that the CHARYBDIS implementation above is particularly suitable for this purpose).

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