// main08.cc is a part of the PYTHIA event generator. // Copyright (C) 2013 Torbjorn Sjostrand. // PYTHIA is licenced under the GNU GPL version 2, see COPYING for details. // Please respect the MCnet Guidelines, see GUIDELINES for details. // This is a simple test program. // It illustrates methods to emphasize generation at high pT. #include "Pythia.h" using namespace Pythia8; int main() { // Different modes are illustrated for setting the pT ranges. // 1 : Hardcoded in the main program. // 2 : Using the Main:subrun keyword in a separate command file. // A third method instead biases selection continuously. // 3 : Bias high-pT selection by a pT^4 factor. // Matching also to low-pT processes is more complicated. // 4 : Matching between low- and high-pT. (No diffraction.) // 5: As 4, but bias high-pT selection by a pT^4 factor. int mode = 5; // Number of events to generate per bin. int nEvent = 100000; // One does not need complete events to study pThard spectrum only. bool completeEvents = false; // Optionally minimize output (almost) to final results. bool smallOutput = true; // Book histograms. int nRange = 100; double pTrange = (mode < 4) ? 1000. : 100.; Hist pTraw("pTHat distribution, unweighted", nRange, 0., pTrange); Hist pTnorm("pTHat distribution, weighted", nRange, 0., pTrange); Hist pTpow3("pTHat distribution, pT3*weighted", nRange, 0., pTrange); Hist pTpow5("pTHat distribution, pT5*weighted", nRange, 0., pTrange); Hist pTnormPart("pTHat distribution, weighted", nRange, 0., pTrange); Hist pTpow3Part("pTHat distribution, pT3*weighted", nRange, 0., pTrange); Hist pTpow5Part("pTHat distribution, pT5*weighted", nRange, 0., pTrange); // Generator. Pythia pythia; // Shorthand for some public members of pythia (also static ones). Settings& settings = pythia.settings; Info& info = pythia.info; // Optionally limit output to minimal one. if (smallOutput) { pythia.readString("Init:showProcesses = off"); pythia.readString("Init:showMultipartonInteractions = off"); pythia.readString("Init:showChangedSettings = off"); pythia.readString("Init:showChangedParticleData = off"); pythia.readString("Next:numberCount = 1000000000"); pythia.readString("Next:numberShowInfo = 0"); pythia.readString("Next:numberShowProcess = 0"); pythia.readString("Next:numberShowEvent = 0"); } // Number of bins to use. In mode 2 read from main08.cmnd file. int nBin = 5; if (mode == 2) { pythia.readFile("main08.cmnd"); nBin = pythia.mode("Main:numberOfSubruns"); } else if (mode == 3) nBin = 1; else if (mode == 4) nBin = 4; else if (mode == 5) nBin = 2; // Mode 1: set up five pT bins - last one open-ended. double pTlimit[6] = {100., 150., 250., 400., 600., 0.}; // Modes 4 & 5: set up pT bins for range [0, 100]. The lowest bin // is generated with soft processes, to regularize pT -> 0 blowup. // Warning: if pTlimitLow[1] is picked too low there will be a // visible discontinuity, since soft processes are generated with // dampening and "Sudakov" for pT -> 0, while hard processes are not. double pTlimitLow[6] = {0., 20., 40., 70., 100.}; double pTlimitTwo[3] = {0., 20., 100.}; // Loop over number of bins, i.e. number of subruns. for (int iBin = 0; iBin < nBin; ++iBin) { // Normally HardQCD, but in two cases minBias. // Need MPI on in minBias to get first interaction, but not else. if (mode > 3 && iBin == 0) { pythia.readString("HardQCD:all = off"); pythia.readString("SoftQCD:minBias = on"); if (!completeEvents) { pythia.readString("PartonLevel:all = on"); pythia.readString("PartonLevel:ISR = off"); pythia.readString("PartonLevel:FSR = off"); pythia.readString("HadronLevel:all = off"); } } else { pythia.readString("HardQCD:all = on"); pythia.readString("SoftQCD:minBias = off"); if (!completeEvents) pythia.readString("PartonLevel:all = off"); } // Mode 1: hardcoded here. Use settings.parm for non-string input. if (mode == 1) { settings.parm("PhaseSpace:pTHatMin", pTlimit[iBin]); settings.parm("PhaseSpace:pTHatMax", pTlimit[iBin + 1]); } // Mode 2: subruns stored in the main08.cmnd file. else if (mode == 2) pythia.readFile("main08.cmnd", iBin); // Mode 3: The whole range in one step, but pT-weighted. else if (mode == 3) { settings.parm("PhaseSpace:pTHatMin", pTlimit[0]); settings.parm("PhaseSpace:pTHatMax", 0.); pythia.readString("PhaseSpace:bias2Selection = on"); pythia.readString("PhaseSpace:bias2SelectionPow = 4."); pythia.readString("PhaseSpace:bias2SelectionRef = 100."); } // Mode 4: hardcoded here. Use settings.parm for non-string input. else if (mode == 4) { settings.parm("PhaseSpace:pTHatMin", pTlimitLow[iBin]); settings.parm("PhaseSpace:pTHatMax", pTlimitLow[iBin + 1]); } // Mode 5: hardcoded here. Use settings.parm for non-string input. // Hard processes in one step, but pT-weighted. else if (mode == 5) { settings.parm("PhaseSpace:pTHatMin", pTlimitTwo[iBin]); settings.parm("PhaseSpace:pTHatMax", pTlimitTwo[iBin + 1]); if (iBin == 1) { pythia.readString("PhaseSpace:bias2Selection = on"); pythia.readString("PhaseSpace:bias2SelectionPow = 4."); pythia.readString("PhaseSpace:bias2SelectionRef = 20."); } } // Initialize for LHC at 14 TeV. pythia.readString("Beams:eCM = 14000."); pythia.init(); // Reset local histograms (that need to be rescaled before added). pTnormPart.null(); pTpow3Part.null(); pTpow5Part.null(); // Begin event loop. for (int iEvent = 0; iEvent < nEvent; ++iEvent) { // Generate events. Quit if failure. if (!pythia.next()) break; // Soft events have no upper pT limit. They therefore overlap // with hard events, and the overlap must be removed by hand. // No overlap for elastic/diffraction, which is only part of soft. double pTHat = info.pTHat(); if (mode > 3 && iBin == 0 && info.isMinBias() && pTHat > pTlimitLow[1]) continue; // Fill hard scale of event. double weight = info.weight(); pTraw.fill( pTHat ); pTnormPart.fill( pTHat, weight); pTpow3Part.fill( pTHat, weight * pow3(pTHat) ); pTpow5Part.fill( pTHat, weight * pow5(pTHat) ); // End of event loop. Statistics. } if (!smallOutput) pythia.stat(); // Normalize to cross section for each case, and add to sum. double sigmaNorm = (info.sigmaGen() / info.weightSum()) * (nRange / pTrange); pTnorm += sigmaNorm * pTnormPart; pTpow3 += sigmaNorm * pTpow3Part; pTpow5 += sigmaNorm * pTpow5Part; // End of pT-bin loop. } // Output histograms. cout << pTraw << pTnorm << pTpow3 << pTpow5; // Done. return 0; }