| | 1 | |
| | 2 | |
| | 3 | === The Pythia package in the MadGraph simulation chain === |
| | 4 | |
| | 5 | |
| | 6 | If the Pythia package is downloaded and compiled and the file Cards/pythia_card.dat exists, Pythia will automatically be run by the generate_events script. To avoid this, just remove the file Cards/pythia_card.dat. |
| | 7 | |
| | 8 | The easiest way to run Pythia on an existing generation is to go to the Events directory and run <br /> |
| | 9 | ../bin/run_pythia path_to_pythia 0 prefix_of_run<br /> |
| | 10 | The second argument is 0 for serial and 1 for cluster running, path_to_pythia is the path to the {{{pythia}}} executable (usually =../../pythia-pgs/src=) and prefix_of_run is the name of the run, i.e. what comes before "''unweighted''events.lhe.gz". |
| | 11 | |
| | 12 | The Pythia package includes the following files and packages: |
| | 13 | |
| | 14 | * !ME2Pythia.f (a Pythia interface to read MadEvent LHE files) |
| | 15 | * pythia.f (the main program) |
| | 16 | * hep2lhe.f (reads STDHEP files and performs jet clustering to produce simplified LHE complient output files) |
| | 17 | * getjet.f (cone jet clustering) |
| | 18 | * ktclusdble.f (kt jet clustering) |
| | 19 | * Pythia 6.4.14 |
| | 20 | * LHAPDF v4r2 |
| | 21 | * !StdHep 5.04.01 |
| | 22 | * Tauola 2.1 (came with PGS 4.0) |
| | 23 | |
| | 24 | The Pythia main program reads the file pythia_card.dat with Pythia run parameters, opens the LHE file unweighted_events.lhe and passes it to event simulation. The output is written in the form of !StdHep files, which store all the Pythia event information in HEPEVT common block format. |
| | 25 | |
| | 26 | The !MadEvent-Pythia interface extracts and reads the MadEvent model parameters and necessary run parameters (including PDF and matching info), initializes Pythia and reads events. It also automatically performs the following actions: |
| | 27 | * Gives the default Pythia mass to massless final state particles from MadEvent, such as muons, electrons and quarks. |
| | 28 | * Adjusts the cross section to account for closed decay channels for final-state particles from MadEvent which are decayed by Pythia |
| | 29 | * If matching is turned on in MadEvent (using ickkw=1 in the run_card.dat), the type of matching is automatically specified and performed. See [:Matching:the matching section] for instructions on how to use the matching implemented in MadEvent and Pythia. |
| | 30 | |
| | 31 | |
| | 32 | ==== The pythia_card.dat ==== |
| | 33 | |
| | 34 | If the pythia-pgs package is downloaded and compiled and the pythia_card.dat exists in the Cards directory, Pythia will automatically be run by the generate_events script. The syntax of the pythia_card.dat is: |
| | 35 | |
| | 36 | parameter=value |
| | 37 | |
| | 38 | Extra spaces can be used, but not tabs. ! or # at the start of lines indicate comments. |
| | 39 | |
| | 40 | The parameters that can be set in the pythia_card.dat are: |
| | 41 | * Any Pythia parameters settings. Examples are MSTP(61) and MSTP(71) (for initial and final state radiation), MSTP(81) (for multiple interactions) and MSTJ(1) for hadronization/fragmentation. If internal processes are turned on using MSEL or MSUB(I) non-zero, Pythia will be run with only internal processes, and the event file is used only to define collider and PDF settings. |
| | 42 | * PSSCALE to choose the showering scale. PSSCALE=0 to use the scale SCALUP given by MadEvent, PSSCALE=1 to use the standard Herwig scale (the minimum dot product of color connected pairs) |
| | 43 | * NITER: number of iterations (-1 for all events in the LHE file) |
| | 44 | |
| | 45 | Parameters relevant for matching: |
| | 46 | * IEXCFILE: 1 for exclusive samples (not including the highest jet multiplicity), 0 for inclusive samples (including the highest jet multiplicity) |
| | 47 | * QCUT. For matching using the kt scheme, this is the jet measure cutoff used by Pythia. If not given, it will be set to max(xqcut+5,xqcut*1.2) (where xqcut is read from the MadEvent run_card.dat) |
| | 48 | * MINJETS: Minimum jet multiplicity included in the matching (default -1: lowest multiplicity in file) |
| | 49 | * MAXJETS: Maximum jet multiplicity included in the matching (default -1: highest multiplicity in file) |
| | 50 | * KTSCHE: The kt clustering scheme used by KTCLUS. Default 4313 for hadron collisions, 1 for e+e- collisions. |
| | 51 | * EXCRES=PDG: Discard event with on-shell resonance PDG in event file. Repeat for additional resonances. |
| | 52 | |
| | 53 | Parameters read by the hep2lhe converter: |
| | 54 | * IJETALG: 1 for cone jets by GETJET, 0 for kt jets by KTCLUS |
| | 55 | * ETCLUS: Minimum clustering scale for kt jets |
| | 56 | * ETMIN: Minimum ET for cone jets |
| | 57 | * RMAX: Maximum Delta(R) for cone jets |
| | 58 | * ETAMAX: Maximum pseudorapidity for particles in detector |
| | 59 | * ETAJETMAX: Maximum rapidity for reconstructed jets |
| | 60 | * NCY: Number of cells in the detector in the pseudorapitidy direction (for GETJET) |
| | 61 | * NCPHI: Number of cells in the detector in the phi direction (for GETJET) |
| | 62 | * KTSCHE: The kt clustering scheme used by KTCLUS. Default 4313. |
| | 63 | |
| | 64 | -- Main.JohanAlwall - 21 Feb 2008 |
