// PowhegHooks.h is a part of the PYTHIA event generator. // Copyright (C) 2017 Richard Corke, Torbjorn Sjostrand. // PYTHIA is licenced under the GNU GPL version 2, see COPYING for details. // Please respect the MCnet Guidelines, see GUIDELINES for details. // Author: Richard Corke. // This class is used to perform a vetoed shower, where emissions // already covered in a POWHEG NLO generator should be omitted. // To first approximation the handover should happen at the SCALE // of the LHA, but since the POWHEG-BOX uses a different pT definition // than PYTHIA, both for ISR and FSR, a more sophisticated treatment // is needed. See the online manual on POWHEG merging for details. #ifndef Pythia8_PowhegHooks_H #define Pythia8_PowhegHooks_H // Includes #include "Pythia8/Pythia.h" namespace Pythia8 { //========================================================================== // Use userhooks to veto PYTHIA emissions above the POWHEG scale. class PowhegHooks : public UserHooks { public: // Constructor and destructor. PowhegHooks() {} ~PowhegHooks() {} //-------------------------------------------------------------------------- // Initialize settings, detailing merging strategy to use. bool initAfterBeams() { nFinal = settingsPtr->mode("POWHEG:nFinal"); vetoMode = settingsPtr->mode("POWHEG:veto"); vetoCount = settingsPtr->mode("POWHEG:vetoCount"); pThardMode = settingsPtr->mode("POWHEG:pThard"); pTemtMode = settingsPtr->mode("POWHEG:pTemt"); emittedMode = settingsPtr->mode("POWHEG:emitted"); pTdefMode = settingsPtr->mode("POWHEG:pTdef"); MPIvetoMode = settingsPtr->mode("POWHEG:MPIveto"); QEDvetoMode = settingsPtr->mode("POWHEG:QEDveto"); return true; } //-------------------------------------------------------------------------- // Routines to calculate the pT (according to pTdefMode) in a splitting: // ISR: i (radiator after) -> j (emitted after) k (radiator before) // FSR: i (radiator before) -> j (emitted after) k (radiator after) // For the Pythia pT definition, a recoiler (after) must be specified. // Compute the Pythia pT separation. Based on pTLund function in History.cc inline double pTpythia(const Event &e, int RadAfterBranch, int EmtAfterBranch, int RecAfterBranch, bool FSR) { // Convenient shorthands for later Vec4 radVec = e[RadAfterBranch].p(); Vec4 emtVec = e[EmtAfterBranch].p(); Vec4 recVec = e[RecAfterBranch].p(); int radID = e[RadAfterBranch].id(); // Calculate virtuality of splitting double sign = (FSR) ? 1. : -1.; Vec4 Q(radVec + sign * emtVec); double Qsq = sign * Q.m2Calc(); // Mass term of radiator double m2Rad = (abs(radID) >= 4 && abs(radID) < 7) ? pow2(particleDataPtr->m0(radID)) : 0.; // z values for FSR and ISR double z, pTnow; if (FSR) { // Construct 2 -> 3 variables Vec4 sum = radVec + recVec + emtVec; double m2Dip = sum.m2Calc(); double x1 = 2. * (sum * radVec) / m2Dip; double x3 = 2. * (sum * emtVec) / m2Dip; z = x1 / (x1 + x3); pTnow = z * (1. - z); } else { // Construct dipoles before/after splitting Vec4 qBR(radVec - emtVec + recVec); Vec4 qAR(radVec + recVec); z = qBR.m2Calc() / qAR.m2Calc(); pTnow = (1. - z); } // Virtuality with correct sign pTnow *= (Qsq - sign * m2Rad); // Can get negative pT for massive splittings if (pTnow < 0.) { cout << "Warning: pTpythia was negative" << endl; return -1.; } // Return pT return sqrt(pTnow); } // Compute the POWHEG pT separation between i and j inline double pTpowheg(const Event &e, int i, int j, bool FSR) { // pT value for FSR and ISR double pTnow = 0.; if (FSR) { // POWHEG d_ij (in CM frame). Note that the incoming beams have not // been updated in the parton systems pointer yet (i.e. prior to any // potential recoil). int iInA = partonSystemsPtr->getInA(0); int iInB = partonSystemsPtr->getInB(0); double betaZ = - ( e[iInA].pz() + e[iInB].pz() ) / ( e[iInA].e() + e[iInB].e() ); Vec4 iVecBst(e[i].p()), jVecBst(e[j].p()); iVecBst.bst(0., 0., betaZ); jVecBst.bst(0., 0., betaZ); pTnow = sqrt( (iVecBst + jVecBst).m2Calc() * iVecBst.e() * jVecBst.e() / pow2(iVecBst.e() + jVecBst.e()) ); } else { // POWHEG pT_ISR is just kinematic pT pTnow = e[j].pT(); } // Check result if (pTnow < 0.) { cout << "Warning: pTpowheg was negative" << endl; return -1.; } return pTnow; } // Calculate pT for a splitting based on pTdefMode. // If j is -1, all final-state partons are tried. // If i, k, r and xSR are -1, then all incoming and outgoing // partons are tried. // xSR set to 0 means ISR, while xSR set to 1 means FSR inline double pTcalc(const Event &e, int i, int j, int k, int r, int xSRin) { // Loop over ISR and FSR if necessary double pTemt = -1., pTnow; int xSR1 = (xSRin == -1) ? 0 : xSRin; int xSR2 = (xSRin == -1) ? 2 : xSRin + 1; for (int xSR = xSR1; xSR < xSR2; xSR++) { // FSR flag bool FSR = (xSR == 0) ? false : true; // If all necessary arguments have been given, then directly calculate. // POWHEG ISR and FSR, need i and j. if ((pTdefMode == 0 || pTdefMode == 1) && i > 0 && j > 0) { pTemt = pTpowheg(e, i, j, (pTdefMode == 0) ? false : FSR); // Pythia ISR, need i, j and r. } else if (!FSR && pTdefMode == 2 && i > 0 && j > 0 && r > 0) { pTemt = pTpythia(e, i, j, r, FSR); // Pythia FSR, need k, j and r. } else if (FSR && pTdefMode == 2 && j > 0 && k > 0 && r > 0) { pTemt = pTpythia(e, k, j, r, FSR); // Otherwise need to try all possible combinations. } else { // Start by finding incoming legs to the hard system after // branching (radiator after branching, i for ISR). // Use partonSystemsPtr to find incoming just prior to the // branching and track mothers. int iInA = partonSystemsPtr->getInA(0); int iInB = partonSystemsPtr->getInB(0); while (e[iInA].mother1() != 1) { iInA = e[iInA].mother1(); } while (e[iInB].mother1() != 2) { iInB = e[iInB].mother1(); } // If we do not have j, then try all final-state partons int jNow = (j > 0) ? j : 0; int jMax = (j > 0) ? j + 1 : e.size(); for (; jNow < jMax; jNow++) { // Final-state only if (!e[jNow].isFinal()) continue; // Exclude photons (and W/Z!) if (QEDvetoMode==0 && e[jNow].colType() == 0) continue; // POWHEG if (pTdefMode == 0 || pTdefMode == 1) { // ISR - only done once as just kinematical pT if (!FSR) { pTnow = pTpowheg(e, iInA, jNow, (pTdefMode == 0) ? false : FSR); if (pTnow > 0.) pTemt = (pTemt < 0) ? pTnow : min(pTemt, pTnow); // FSR - try all outgoing partons from system before branching // as i. Note that for the hard system, there is no // "before branching" information. } else { int outSize = partonSystemsPtr->sizeOut(0); for (int iMem = 0; iMem < outSize; iMem++) { int iNow = partonSystemsPtr->getOut(0, iMem); // i != jNow and no carbon copies if (iNow == jNow ) continue; // Exclude photons (and W/Z!) if (QEDvetoMode==0 && e[iNow].colType() == 0) continue; if (jNow == e[iNow].daughter1() && jNow == e[iNow].daughter2()) continue; pTnow = pTpowheg(e, iNow, jNow, (pTdefMode == 0) ? false : FSR); if (pTnow > 0.) pTemt = (pTemt < 0) ? pTnow : min(pTemt, pTnow); } // for (iMem) } // if (!FSR) // Pythia } else if (pTdefMode == 2) { // ISR - other incoming as recoiler if (!FSR) { pTnow = pTpythia(e, iInA, jNow, iInB, FSR); if (pTnow > 0.) pTemt = (pTemt < 0) ? pTnow : min(pTemt, pTnow); pTnow = pTpythia(e, iInB, jNow, iInA, FSR); if (pTnow > 0.) pTemt = (pTemt < 0) ? pTnow : min(pTemt, pTnow); // FSR - try all final-state coloured partons as radiator // after emission (k). } else { for (int kNow = 0; kNow < e.size(); kNow++) { if (kNow == jNow || !e[kNow].isFinal()) continue; if (QEDvetoMode==0 && e[kNow].colType() == 0) continue; // For this kNow, need to have a recoiler. // Try two incoming. pTnow = pTpythia(e, kNow, jNow, iInA, FSR); if (pTnow > 0.) pTemt = (pTemt < 0) ? pTnow : min(pTemt, pTnow); pTnow = pTpythia(e, kNow, jNow, iInB, FSR); if (pTnow > 0.) pTemt = (pTemt < 0) ? pTnow : min(pTemt, pTnow); // Try all other outgoing. for (int rNow = 0; rNow < e.size(); rNow++) { if (rNow == kNow || rNow == jNow || !e[rNow].isFinal()) continue; if(QEDvetoMode==0 && e[rNow].colType() == 0) continue; pTnow = pTpythia(e, kNow, jNow, rNow, FSR); if (pTnow > 0.) pTemt = (pTemt < 0) ? pTnow : min(pTemt, pTnow); } // for (rNow) } // for (kNow) } // if (!FSR) } // if (pTdefMode) } // for (j) } } // for (xSR) return pTemt; } //-------------------------------------------------------------------------- // Extraction of pThard based on the incoming event. // Assume that all the final-state particles are in a continuous block // at the end of the event and the final entry is the POWHEG emission. // If there is no POWHEG emission, then pThard is set to SCALUP. inline bool canVetoMPIStep() { return true; } inline int numberVetoMPIStep() { return 1; } inline bool doVetoMPIStep(int nMPI, const Event &e) { // Extra check on nMPI if (nMPI > 1) return false; // Find if there is a POWHEG emission. Go backwards through the // event record until there is a non-final particle. Also sum pT and // find pT_1 for possible MPI vetoing int count = 0; double pT1 = 0., pTsum = 0.; for (int i = e.size() - 1; i > 0; i--) { if (e[i].isFinal()) { count++; pT1 = e[i].pT(); pTsum += e[i].pT(); } else break; } // Extra check that we have the correct final state if (count != nFinal && count != nFinal + 1) { cout << "Error: wrong number of final state particles in event" << endl; exit(1); } // Flag if POWHEG radiation present and index isEmt = (count == nFinal) ? false : true; int iEmt = (isEmt) ? e.size() - 1 : -1; // If there is no radiation or if pThardMode is 0 then set pThard = SCALUP. if (!isEmt || pThardMode == 0) { pThard = infoPtr->scalup(); // If pThardMode is 1 then the pT of the POWHEG emission is checked against // all other incoming and outgoing partons, with the minimal value taken } else if (pThardMode == 1) { pThard = pTcalc(e, -1, iEmt, -1, -1, -1); // If pThardMode is 2, then the pT of all final-state partons is checked // against all other incoming and outgoing partons, with the minimal value // taken } else if (pThardMode == 2) { pThard = pTcalc(e, -1, -1, -1, -1, -1); } // Find MPI veto pT if necessary if (MPIvetoMode == 1) { pTMPI = (isEmt) ? pTsum / 2. : pT1; } // Initialise other variables accepted = false; nAcceptSeq = nISRveto = nFSRveto = 0; // Do not veto the event return false; } //-------------------------------------------------------------------------- // ISR veto inline bool canVetoISREmission() { return (vetoMode == 0) ? false : true; } inline bool doVetoISREmission(int, const Event &e, int iSys) { // Must be radiation from the hard system if (iSys != 0) return false; // If we already have accepted 'vetoCount' emissions in a row, do nothing if (vetoMode == 1 && nAcceptSeq >= vetoCount) return false; // Pythia radiator after, emitted and recoiler after. int iRadAft = -1, iEmt = -1, iRecAft = -1; for (int i = e.size() - 1; i > 0; i--) { if (iRadAft == -1 && e[i].status() == -41) iRadAft = i; else if (iEmt == -1 && e[i].status() == 43) iEmt = i; else if (iRecAft == -1 && e[i].status() == -42) iRecAft = i; if (iRadAft != -1 && iEmt != -1 && iRecAft != -1) break; } if (iRadAft == -1 || iEmt == -1 || iRecAft == -1) { e.list(); cout << "Error: couldn't find Pythia ISR emission" << endl; exit(1); } // pTemtMode == 0: pT of emitted w.r.t. radiator // pTemtMode == 1: min(pT of emitted w.r.t. all incoming/outgoing) // pTemtMode == 2: min(pT of all outgoing w.r.t. all incoming/outgoing) int xSR = (pTemtMode == 0) ? 0 : -1; int i = (pTemtMode == 0) ? iRadAft : -1; int j = (pTemtMode != 2) ? iEmt : -1; int k = -1; int r = (pTemtMode == 0) ? iRecAft : -1; double pTemt = pTcalc(e, i, j, k, r, xSR); // If a Born configuration, and a photon, and QEDvetoMode=2, // then don't veto photons, W, or Z harder than pThard bool vetoParton = (!isEmt && e[iEmt].colType()==0 && QEDvetoMode==2) ? false: true; // Veto if pTemt > pThard if (pTemt > pThard) { if(!vetoParton) { // Don't veto ANY emissions afterwards nAcceptSeq = vetoCount-1; } else { nAcceptSeq = 0; nISRveto++; return true; } } // Else mark that an emission has been accepted and continue nAcceptSeq++; accepted = true; return false; } //-------------------------------------------------------------------------- // FSR veto inline bool canVetoFSREmission() { return (vetoMode == 0) ? false : true; } inline bool doVetoFSREmission(int, const Event &e, int iSys, bool) { // Must be radiation from the hard system if (iSys != 0) return false; // If we already have accepted 'vetoCount' emissions in a row, do nothing if (vetoMode == 1 && nAcceptSeq >= vetoCount) return false; // Pythia radiator (before and after), emitted and recoiler (after) int iRecAft = e.size() - 1; int iEmt = e.size() - 2; int iRadAft = e.size() - 3; int iRadBef = e[iEmt].mother1(); if ( (e[iRecAft].status() != 52 && e[iRecAft].status() != -53) || e[iEmt].status() != 51 || e[iRadAft].status() != 51) { e.list(); cout << "Error: couldn't find Pythia FSR emission" << endl; exit(1); } // Behaviour based on pTemtMode: // 0 - pT of emitted w.r.t. radiator before // 1 - min(pT of emitted w.r.t. all incoming/outgoing) // 2 - min(pT of all outgoing w.r.t. all incoming/outgoing) int xSR = (pTemtMode == 0) ? 1 : -1; int i = (pTemtMode == 0) ? iRadBef : -1; int k = (pTemtMode == 0) ? iRadAft : -1; int r = (pTemtMode == 0) ? iRecAft : -1; // When pTemtMode is 0 or 1, iEmt has been selected double pTemt = 0.; if (pTemtMode == 0 || pTemtMode == 1) { // Which parton is emitted, based on emittedMode: // 0 - Pythia definition of emitted // 1 - Pythia definition of radiated after emission // 2 - Random selection of emitted or radiated after emission // 3 - Try both emitted and radiated after emission int j = iRadAft; if (emittedMode == 0 || (emittedMode == 2 && rndmPtr->flat() < 0.5)) j++; for (int jLoop = 0; jLoop < 2; jLoop++) { if (jLoop == 0) pTemt = pTcalc(e, i, j, k, r, xSR); else if (jLoop == 1) pTemt = min(pTemt, pTcalc(e, i, j, k, r, xSR)); // For emittedMode == 3, have tried iRadAft, now try iEmt if (emittedMode != 3) break; if (k != -1) swap(j, k); else j = iEmt; } // If pTemtMode is 2, then try all final-state partons as emitted } else if (pTemtMode == 2) { pTemt = pTcalc(e, i, -1, k, r, xSR); } // If a Born configuration, and a photon, and QEDvetoMode=2, // then don't veto photons, W's or Z's harder than pThard bool vetoParton = (!isEmt && e[iEmt].colType()==0 && QEDvetoMode==2) ? false: true; // Veto if pTemt > pThard if (pTemt > pThard) { if(!vetoParton) { // Don't veto ANY emissions afterwards nAcceptSeq = vetoCount-1; } else { nAcceptSeq = 0; nFSRveto++; return true; } } // Else mark that an emission has been accepted and continue nAcceptSeq++; accepted = true; return false; } //-------------------------------------------------------------------------- // MPI veto inline bool canVetoMPIEmission() {return (MPIvetoMode == 0) ? false : true;} inline bool doVetoMPIEmission(int, const Event &e) { if (MPIvetoMode == 1) { if (e[e.size() - 1].pT() > pTMPI) return true; } return false; } //-------------------------------------------------------------------------- // Functions to return information inline int getNISRveto() { return nISRveto; } inline int getNFSRveto() { return nFSRveto; } //-------------------------------------------------------------------------- private: int nFinal, vetoMode, vetoCount, pThardMode, pTemtMode, emittedMode, pTdefMode, MPIvetoMode, QEDvetoMode; double pThard, pTMPI; bool accepted, isEmt; // The number of accepted emissions (in a row) // Flag for PowHeg Born or Radiation int nAcceptSeq; // Statistics on vetos unsigned long int nISRveto, nFSRveto; }; //========================================================================== } // end namespace Pythia8 #endif // end Pythia8_PowhegHooks_H