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The implementation of medium-effects in parton shower Monte Carlo codes can be downloaded at this web site. At the moment this implementation is available only for PYTHIA. A version for HERWIG will come soon.

Technically, the implementation corresponds to a modification of the final state radiation routines within both event generators.

The codes, in fortran, are not official releases of PYTHIA or HERWIG. Our modifications run on top of their default routines and options. The resulting codes that we provide are nicknamed Q-PYTHIA and Q-HERWIG.


Concerning Q-PYTHIA, only two routines (QPYGIN and QPYGEO) containing the information about the medium properties need to be modified by the user - see the corresponding header of these routines.

Two options are offered:

1. A separate file for the modified PYSHOW plus auxiliary routines along with QPYGIN and QPYGEO. The file is named q-pyshow.1.0.f .

2. One single file (q-pythia.1.0.f) containing the whole PYTHIA v6.4.18 with all modifications inside.

Besides, a data file called grid-qp.dat must also be available in the working directory and an example to run Q-PYTHIA is provided in the file main-q-pythia.1.0.f. The corresponding fortran codes need to be linked with the CERNLIB libraries.

When using Q-PYTHIA, please quote:

N. Armesto, L. Cunqueiro and C. A. Salgado, Eur. Phys. J. C63 (2009) 679 [arXiv:0907.1014 [hep-ph]].

where a short manual can be found, and the PYTHIA 6.4 manual

T. Sjostrand, S. Mrenna and P. Skands, JHEP 0605 (2006) 026 [hep-ph/0603175].



v1.0: Q-PYTHIAv1.0 code

v1.0.1: Q-PYTHIAv1.0.1 code: no need to link with the CERNLIB libraries.

v1.0.2: Q-PYTHIAv1.0.2 code: possible problem of multiple calls to qpygin fixed. Now the user must call new routine qpygin0 once per nucleon-nucleon collision (see the examples of main's) and define there the initial position and time in the cms of the collision. Do not touch qpygin which automatically makes the boost and rotation to the cms of the hard scattering. Routine qpyrobo has been included in q-pyshow.1.0.2.f and q-pythia.1.0.2.f. Note that multiple hard interactions break collinear factorization; they can be avoided by setting MSTP(81)=0 in the main program. We thank ShinIchi Esumi for feedback on this point.

v1.0.3: Q-PYTHIAv1.0.3 code: problem with interference with ISR solved.