1 | // main53.cc is a part of the PYTHIA event generator. |
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2 | // Copyright (C) 2012 Peter Skands, Torbjorn Sjostrand. |
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3 | // PYTHIA is licenced under the GNU GPL version 2, see COPYING for details. |
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4 | // Please respect the MCnet Guidelines, see GUIDELINES for details. |
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5 | |
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6 | // This is a simple test program. |
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7 | // It illustrates how to interface an external process with an incoming photon |
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8 | // in a hadron beam, using the MRST2004QED PDF set. |
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9 | // All input apart from the name of the external LHEF file is specified in the |
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10 | // main53.cmnd file. |
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11 | |
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12 | #include "Pythia.h" |
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13 | |
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14 | using namespace Pythia8; |
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15 | |
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16 | int main() { |
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17 | |
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18 | // Generator. Shorthand for the event. |
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19 | Pythia pythia; |
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20 | Event& event = pythia.event; |
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21 | |
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22 | // Read in commands from external file. |
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23 | pythia.readFile("main53.cmnd"); |
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24 | |
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25 | // Extract settings to be used in the main program. |
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26 | int nEvent = pythia.mode("Main:numberOfEvents"); |
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27 | |
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28 | // Initialize. Either of two opions, to be picked in main53.cmnd. |
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29 | // 1) Read in external event with incoming photon in the ME, |
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30 | // from pre-generated .lhe file (thanks to SANC and R. Sadykov). |
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31 | // 2) Use internal fermion gamma -> W+- fermion' process. |
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32 | pythia.init(); |
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33 | |
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34 | // Histograms for pT distribution in gluon production vertex. |
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35 | Hist pTprim( "pT of photon production, no ISR", 100, 0., 100.); |
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36 | Hist pTwith( "pT of photon production, with ISR", 100, 0., 100.); |
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37 | |
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38 | // Begin event loop. |
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39 | for (int iEvent = 0; iEvent < nEvent; ++iEvent) { |
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40 | |
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41 | // Generate events. Quit if failure. |
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42 | if (!pythia.next()) { |
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43 | break; |
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44 | } |
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45 | |
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46 | // Analyze event to find branching where photon is produced. |
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47 | int iGam = (event[3].id() == 22) ? 3 : 4; |
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48 | int iGamMother = iGam; |
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49 | for ( ; ; ) { |
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50 | iGamMother = event[iGam].mother1(); |
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51 | if (iGamMother < iGam || event[iGamMother].id() != 22) break; |
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52 | iGam = iGamMother; |
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53 | } |
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54 | |
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55 | // Find and histogram pT in this branching. |
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56 | if (iGamMother < iGam) pTprim.fill( event[iGam].pT() ); |
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57 | else { |
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58 | int iQ = iGamMother; |
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59 | int size = event.size(); |
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60 | do ++iQ; |
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61 | while (event[iQ].status() != -43 && iQ < size - 1); |
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62 | if (event[iQ].status() == -43) pTwith.fill( event[iQ].pT() ); |
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63 | } |
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64 | |
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65 | // End of event loop. |
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66 | } |
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67 | |
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68 | // Final statistics and histogram output. |
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69 | pythia.stat(); |
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70 | cout << pTprim << pTwith; |
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71 | |
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72 | return 0; |
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73 | } |
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74 | |
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