// main21.cc is a part of the PYTHIA event generator. // Copyright (C) 2010 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 how to feed in a single particle // or a toy parton-level configurations. #include "Pythia.h" using namespace Pythia8; //========================================================================== // Single-particle gun. The particle must be a colour singlet. // Input: flavour, energy, direction (theta, phi). // If theta < 0 then random choice over solid angle. void fillParticle(int id, double ee, double thetaIn, double phiIn, Event& event, ParticleData& pdt, Rndm& rndm) { // Reset event record to allow for new event. event.reset(); // Select particle mass; where relevant according to Breit-Wigner. double mm = pdt.mass(id); double pp = sqrtpos(ee*ee - mm*mm); // Angles as input or uniform in solid angle. double cThe, sThe, phi; if (thetaIn >= 0.) { cThe = cos(thetaIn); sThe = sin(thetaIn); phi = phiIn; } else { cThe = 2. * rndm.flat() - 1.; sThe = sqrtpos(1. - cThe * cThe); phi = 2. * M_PI * rndm.flat(); } // Store the particle in the event record. event.append( id, 1, 0, 0, pp * sThe * cos(phi), pp * sThe * sin(phi), pp * cThe, ee, mm); } //========================================================================== // Simple method to do the filling of partons into the event record. void fillPartons(int type, double ee, Event& event, ParticleData& pdt, Rndm& rndm) { // Reset event record to allow for new event. event.reset(); // Information on a q qbar system, to be hadronized. if (type == 1) { int id = 2; double mm = pdt.m0(id); double pp = sqrtpos(ee*ee - mm*mm); event.append( id, 23, 101, 0, 0., 0., pp, ee, mm); event.append( -id, 23, 0, 101, 0., 0., -pp, ee, mm); // Information on a g g system, to be hadronized. } else if (type == 2) { event.append( 21, 23, 101, 102, 0., 0., ee, ee); event.append( 21, 23, 102, 101, 0., 0., -ee, ee); // Information on a g g g system, to be hadronized. } else if (type == 3) { event.append( 21, 23, 101, 102, 0., 0., ee, ee); event.append( 21, 23, 102, 103, 0.8 * ee, 0., -0.6 * ee, ee); event.append( 21, 23, 103, 101, -0.8 * ee, 0., -0.6 * ee, ee); // Information on a q q q junction system, to be hadronized. } else if (type == 4 || type == 5) { // Need a colour singlet mother parton to define junction origin. event.append( 1000022, -21, 0, 0, 2, 4, 0, 0, 0., 0., 1.01 * ee, 1.01 * ee); // The three endpoint q q q; the minimal system. double rt75 = sqrt(0.75); event.append( 2, 23, 1, 0, 0, 0, 101, 0, 0., 0., 1.01 * ee, 1.01 * ee); event.append( 2, 23, 1, 0, 0, 0, 102, 0, rt75 * ee, 0., -0.5 * ee, ee ); event.append( 1, 23, 1, 0, 0, 0, 103, 0, -rt75 * ee, 0., -0.5 * ee, ee ); // Define the qqq configuration as starting point for adding gluons. if (type == 5) { int colNow[4] = {0, 101, 102, 103}; Vec4 pQ[4]; pQ[1] = Vec4(0., 0., 1., 0.); pQ[2] = Vec4( rt75, 0., -0.5, 0.); pQ[3] = Vec4(-rt75, 0., -0.5, 0.); // Minimal cos(q-g opening angle), allows more or less nasty events. double cosThetaMin =0.; // Add a few gluons (almost) at random. for (int nglu = 0; nglu < 5; ++nglu) { int iq = 1 + int( 2.99999 * rndm.flat() ); double px, py, pz, e, prod; do { e = ee * rndm.flat(); double cThe = 2. * rndm.flat() - 1.; double phi = 2. * M_PI * rndm.flat(); px = e * sqrt(1. - cThe*cThe) * cos(phi); py = e * sqrt(1. - cThe*cThe) * sin(phi); pz = e * cThe; prod = ( px * pQ[iq].px() + py * pQ[iq].py() + pz * pQ[iq].pz() ) / e; } while (prod < cosThetaMin); int colNew = 104 + nglu; event.append( 21, 23, 1, 0, 0, 0, colNew, colNow[iq], px, py, pz, e, 0.); colNow[iq] = colNew; } // Update daughter range of mother. event[1].daughters(1, event.size() - 1); } // Information on a q q qbar qbar dijunction system, to be hadronized. } else if (type >= 6) { // The two fictitious beam remnant particles; needed for junctions. event.append( 2212, -12, 0, 0, 3, 5, 0, 0, 0., 0., ee, ee, 0.); event.append(-2212, -12, 0, 0, 6, 8, 0, 0, 0., 0., ee, ee, 0.); // Opening angle between "diquark" legs. double theta = 0.2; double cThe = cos(theta); double sThe = sin(theta); // Set one colour depending on whether more gluons or not. int acol = (type == 6) ? 103 : 106; // The four endpoint q q qbar qbar; the minimal system. // Two additional fictitious partons to make up original beams. event.append( 2, 23, 1, 0, 0, 0, 101, 0, ee * sThe, 0., ee * cThe, ee, 0.); event.append( 1, 23, 1, 0, 0, 0, 102, 0, -ee * sThe, 0., ee * cThe, ee, 0.); event.append( 2, -21, 1, 0, 0, 0, 103, 0, 0., 0., ee , ee, 0.); event.append( -2, 23, 2, 0, 0, 0, 0, 104, ee * sThe, 0., -ee * cThe, ee, 0.); event.append( -1, 23, 2, 0, 0, 0, 0, 105, -ee * sThe, 0., -ee * cThe, ee, 0.); event.append( -2, -21, 2, 0, 0, 0, 0, acol, 0., 0., -ee , ee, 0.); // Add extra gluons on string between junctions. if (type == 7) { event.append( 21, 23, 5, 8, 0, 0, 103, 106, 0., ee, 0., ee, 0.); } else if (type == 8) { event.append( 21, 23, 5, 8, 0, 0, 103, 108, 0., ee, 0., ee, 0.); event.append( 21, 23, 5, 8, 0, 0, 108, 106, 0.,-ee, 0., ee, 0.); } else if (type == 9) { event.append( 21, 23, 5, 8, 0, 0, 103, 107, 0., ee, 0., ee, 0.); event.append( 21, 23, 5, 8, 0, 0, 107, 108, ee, 0., 0., ee, 0.); event.append( 21, 23, 5, 8, 0, 0, 108, 106, 0.,-ee, 0., ee, 0.); } else if (type == 10) { event.append( 21, 23, 5, 8, 0, 0, 103, 107, 0., ee, 0., ee, 0.); event.append( 21, 23, 5, 8, 0, 0, 107, 108, ee, 0., 0., ee, 0.); event.append( 21, 23, 5, 8, 0, 0, 108, 109, 0.,-ee, 0., ee, 0.); event.append( 21, 23, 5, 8, 0, 0, 109, 106,-ee, 0., 0., ee, 0.); } // No more cases: done. } } //========================================================================== int main() { // Pick kind of events to generate: // 0 = single-particle gun. // 1 = q qbar. // 2 = g g. // 3 = g g g. // 4 = minimal q q q junction topology. // 5 = q q q junction topology with gluons on the strings. // 6 = q q qbar qbar dijunction topology, no gluons. // 7 - 10 : ditto, but with 1 - 4 gluons on string between junctions. int type = 0; // Set particle species and energy for single-particle gun. int idGun = 15; double eeGun = 20.; // Set typical energy per parton. double ee = 20.0; // Set number of events to generate and to list. int nEvent = 10000; int nList = 3; // Generator; shorthand for event and particleData. Pythia pythia; Event& event = pythia.event; ParticleData& pdt = pythia.particleData; // Key requirement: switch off ProcessLevel, and thereby also PartonLevel. pythia.readString("ProcessLevel:all = off"); // Optionally switch off decays. //pythia.readString("HadronLevel:Decay = off"); // Provide printout of initial information. pythia.settings.listChanged(); // Initialize. pythia.init(); // Book histograms. Hist epCons("deviation from energy-momentum conservation",100,0.,1e-4); Hist chgCons("deviation from charge conservation",57,-9.5,9.5); Hist nFinal("final particle multiplicity",100,-0.5,99.5); Hist dnparticledp("dn/dp for particles",100,0.,ee); Hist status85("multiplicity status code 85",50,-0.5,49.5); Hist status86("multiplicity status code 86",50,-0.5,49.5); Hist status83("multiplicity status code 83",50,-0.5,49.5); Hist status84("multiplicity status code 84",50,-0.5,49.5); Hist dndtheta("particle flow in event plane",100,-M_PI,M_PI); Hist dedtheta("energy flow in event plane",100,-M_PI,M_PI); Hist dpartondtheta("parton flow in event plane",100,-M_PI,M_PI); Hist dndyAnti("dn/dy primaries antijunction",100, -10., 10.); Hist dndyJun("dn/dy primaries junction",100, -10., 10.); Hist dndySum("dn/dy all primaries",100, -10., 10.); // Begin of event loop. for (int iEvent = 0; iEvent < nEvent; ++iEvent) { if (iEvent%(max(1,nEvent/20)) == 0) cout << " Now begin event " << iEvent << endl; // Set up single particle, with random direction in solid angle. if (type == 0) fillParticle( idGun, eeGun, -1., 0., event, pdt, pythia.rndm); // Set up parton-level configuration. else fillPartons( type, ee, event, pdt, pythia.rndm); // Generate events. Quit if failure. if (!pythia.next()) { cout << " Event generation aborted prematurely, owing to error!\n"; break; } // List first few events. if (iEvent < nList) { event.list(); // Also list junctions. event.listJunctions(); } // Initialize statistics. Vec4 pSum = - event[0].p(); double chargeSum = 0.; if (type == 0) chargeSum = -event[1].charge(); if (type == 4 || type == 5) chargeSum = -1; int nFin = 0; int n85 = 0; int n86 = 0; int n83 = 0; int n84 = 0; // Loop over all particles. for (int i = 0; i < event.size(); ++i) { int status = event[i].statusAbs(); // Find any unrecognized particle codes. int id = event[i].id(); if (id == 0 || !pdt.isParticle(id)) cout << " Error! Unknown code id = " << id << "\n"; // Find particles with E-p mismatch. double eCalc = event[i].eCalc(); if (abs(eCalc/event[i].e() - 1.) > 1e-6) cout << " e mismatch, i = " << i << " e_nominal = " << event[i].e() << " e-from-p = " << eCalc << " m-from-e " << event[i].mCalc() << "\n"; // Parton flow in event plane. if (status == 71 || status == 72) { double thetaXZ = event[i].thetaXZ(); dpartondtheta.fill(thetaXZ); } // Origin of primary hadrons. if (status == 85) ++n85; if (status == 86) ++n86; if (status == 83) ++n83; if (status == 84) ++n84; // Flow of primary hadrons in the event plane. if (status > 80 && status < 90) { double eAbs = event[i].e(); if (eAbs < 0.) {cout << " e < 0 line " << i; event.list();} double thetaXZ = event[i].thetaXZ(); dndtheta.fill(thetaXZ); dedtheta.fill(thetaXZ, eAbs); // Rapidity distribution of primary hadrons. double y = event[i].y(); dndySum.fill(y); if (type >= 6) { int motherId = event[event[i].mother1()].id(); if (motherId > 0 ) dndyJun.fill(event[i].y()); else dndyAnti.fill(event[i].y()); } } // Study final-state particles. if (event[i].isFinal()) { pSum += event[i].p(); chargeSum += event[i].charge(); nFin++; double pAbs = event[i].pAbs(); dnparticledp.fill(pAbs); } } // Fill histograms once for each event. double epDev = abs(pSum.e()) + abs(pSum.px()) + abs(pSum.py()) + abs(pSum.pz()); epCons.fill(epDev); chgCons.fill(chargeSum); nFinal.fill(nFin); status85.fill(n85); status86.fill(n86); status83.fill(n83); status84.fill(n84); if (epDev > 1e-3 || abs(chargeSum) > 0.1) event.list(); // End of event loop. } // Print statistics, histograms and done. pythia.statistics(); cout << epCons << chgCons << nFinal << dnparticledp << dndtheta << dedtheta << dpartondtheta << dndySum; if (type >= 4) cout << status85 << status86 << status83 << status84; if (type >= 6) cout << dndyJun << dndyAnti; // Done. return 0; }