PYTHIA8 Box Generator: Minimum-Bias Events with Injected π⁰/η Decays

MC/config/PWGHF/external/generator/selectNonHfe.C

@@ -1,10 +1,3 @@
-/// Select π⁰ and η within a given rapidity window for enhancement
-/// pdgPartForAccCut: PDG of the particle to select (111=π⁰, 221=η)
-/// minNb: minimum number of such particles per event for enhancement
-
-////  authors: Rashi Gupta (rashi.gupta@cern.ch)
-///  authors: Ravindra Singh (ravindra.singh@cern.ch)
-
 
 #if !defined(__CLING__) || defined(__ROOTCLING__)
 #include "FairGenerator.h"
@@ -14,83 +7,117 @@
 #include "TParticlePDG.h"
 #include "TDatabasePDG.h"
 #include "TMath.h"
+#include <fairlogger/Logger.h>
 #include <cmath>
 #include <vector>
 #endif
 
 #include "Pythia8/Pythia.h"
-using namespace Pythia8;
 
 class GeneratorPythia8Box : public o2::eventgen::GeneratorPythia8
 {
 public:
-
-  GeneratorPythia8Box(std::vector<int> pdgList, int nInject = 3, float ptMin = 0.1, float ptMax = 50.0, float etaMin = -0.8, float etaMax = 0.8) 
-    : mPdgList(pdgList), nParticles(nInject), genMinPt(ptMin), genMaxPt(ptMax), genMinEta(etaMin), genMaxEta(etaMax)
+
+  GeneratorPythia8Box(std::vector<int> pdgList, int nInject = 3,
+                      float ptMin = 0.1, float ptMax = 50.0,
+                      float etaMin = -0.8, float etaMax = 0.8)
+    : mPdgList(pdgList), nParticles(nInject),
+      genMinPt(ptMin), genMaxPt(ptMax),
+      genMinEta(etaMin), genMaxEta(etaMax)
   {
+    // Initialize dedicated Pythia instance for injection/decay only
+    // Reuses same config as main Pythia; beam settings are ignored by moreDecays()
+    auto& param = o2::eventgen::GeneratorPythia8Param::Instance();
+    std::string cfg = gSystem->ExpandPathName(param.config.c_str());
+    if (!mPythiaGun.readFile(cfg, true)) {
+      LOG(fatal) << "Failed to read config for mPythiaGun: " << cfg;
+    }
+    if (!mPythiaGun.init()) {
+      LOG(fatal) << "Failed to init mPythiaGun";
+    }
   }
 
   ~GeneratorPythia8Box() = default;
 
-Bool_t generateEvent() override
-{
-  bool hasElectron = false; 
-
-  while (!hasElectron) {
-    mPythia.event.reset();
+  bool Init() override
+  {
+    return o2::eventgen::GeneratorPythia8::Init();
+  }
 
-    for (int i{0}; i < nParticles; ++i)
-    {
-      int currentPdg = mPdgList[gRandom->Integer(mPdgList.size())];
-      double mass = TDatabasePDG::Instance()->GetParticle(currentPdg)->Mass();
+protected:
 
-      const double pt = gRandom->Uniform(genMinPt, genMaxPt);
-      const double eta = gRandom->Uniform(genMinEta, genMaxEta);
-      const double phi = gRandom->Uniform(0, TMath::TwoPi());
+  // ── generateEvent: MB + injection ──
+  Bool_t generateEvent() override
+  {
+    bool hasElectron = false;
+
+    while (!hasElectron) {
+      // ===== 1. Generate minimum-bias event =====
+      if (!mPythia.next()) continue;
+
+      // ===== 2. Inject π⁰/η into separate gun, decay only them =====
+      mPythiaGun.event.reset();
+      for (int i = 0; i < nParticles; ++i) {
+        int pdg = mPdgList[gRandom->Integer(mPdgList.size())];
+        auto* pPDG = TDatabasePDG::Instance()->GetParticle(pdg);
+        if (!pPDG) continue;
+        double mass = pPDG->Mass();
+
+        double pt  = gRandom->Uniform(genMinPt, genMaxPt);
+        double eta = gRandom->Uniform(genMinEta, genMaxEta);
+        double phi = gRandom->Uniform(0., TMath::TwoPi());
+        double px = pt * cos(phi);
+        double py = pt * sin(phi);
+        double pz = pt * sinh(eta);
+        double e  = sqrt(px * px + py * py + pz * pz + mass * mass);
+
+        mPythiaGun.event.append(pdg, 11, 0, 0, px, py, pz, e, mass);
+      }
 
-      const double px{pt * std::cos(phi)};
-      const double py{pt * std::sin(phi)};
-      const double pz{pt * std::sinh(eta)};
-      const double et{std::hypot(std::hypot(pt, pz), mass)};
+      mPythiaGun.moreDecays();
 
-
-      mPythia.event.append(currentPdg, 11, 0, 0, px, py, pz, et, mass);
+      // ===== 3. Check for electron from injection in acceptance =====
+      for (int i = 0; i < mPythiaGun.event.size(); ++i) {
+        auto& part = mPythiaGun.event[i];
+        if (std::abs(part.id()) == 11 && part.isFinal()) {
+          if (part.pT() > 0.1 && std::abs(part.eta()) < 1.2) {
+            hasElectron = true;
+            break;
+          }
+        }
+      }
     }
 
-
-    if (!mPythia.next()) continue;
+    // ===== 4. Copy injection products to MB event with index offset =====
+    int offset = mPythia.event.size();
 
-
-    for (int i = 0; i < mPythia.event.size(); ++i) {
-      if (std::abs(mPythia.event[i].id()) == 11) {
-
-
-        double childPt = mPythia.event[i].pT();
-        double childEta = mPythia.event[i].eta();
-
-        if (childPt > 0.1 && std::abs(childEta) < 1.2) {
-          hasElectron = true; // Mil gaya!
-          break; 
-        }
-      }
+    for (int i = 0; i < mPythiaGun.event.size(); ++i) {
+      auto part = mPythiaGun.event[i];
+      if (part.id() == 90) continue;            // skip system placeholder
+      if (!part.isFinal() && part.id() != 111 && part.id() != 221) continue;
+
+      if (part.mother1() > 0)   part.mother1(part.mother1()   + offset - 1);
+      if (part.mother2() > 0)   part.mother2(part.mother2()   + offset - 1);
+      if (part.daughter1() > 0) part.daughter1(part.daughter1() + offset - 1);
+      if (part.daughter2() > 0) part.daughter2(part.daughter2() + offset - 1);
+
+      mPythia.event.append(part);
     }
-
-  }
 
-  return true; 
-}
+    return true;
+  }
 
 private:
   std::vector<int> mPdgList;
   double genMinPt, genMaxPt;
   double genMinEta, genMaxEta;
   int nParticles;
+
+  Pythia8::Pythia mPythiaGun;
 };
 
-
 FairGenerator *generatePythia8Box(float ptMin = 0.1, float ptMax = 50.0)
 {
-
   std::vector<int> pdgList = {111, 221};
   return new GeneratorPythia8Box(pdgList, 3, ptMin, ptMax, -0.8, 0.8);
-}
+}

MC/config/PWGHF/hybrid/GeneratorHF_Non_Hfe.json

@@ -1,40 +0,0 @@
-{
-  "generators": [
-    {
-      "name": "pythia8",
-      "config": {
-        "config": "${O2DPG_MC_CONFIG_ROOT}/MC/config/common/pythia8/generator/pythia8_NonHfe.cfg"
-      },
-      "triggers": {
-        "mode": "or",
-        "specs": [
-          {
-            "macro": "${O2DPG_MC_CONFIG_ROOT}/MC/config/PWGHF/trigger/selectNonHfe.C",
-            "function": "selectPionEtaWithinAcc(\"111;221\",-1.5,1.5,1)"
-          }
-        ]
-      }
-    },
-    {
-      "name": "boxgen",
-      "config": {
-        "pdg": 111,
-        "prange[0]": 0.1,
-        "prange[1]": 50.0,
-        "eta[0]": -0.8,
-        "eta[1]": 0.8
-      }
-    },
-    {
-      "name": "boxgen",
-      "config": {
-        "pdg": 221,
-        "prange[0]": 0.1,
-        "prange[1]": 50.0,
-        "eta[0]": -0.8,
-        "eta[1]": 0.8
-      }
-    }
-  ],
-  "fractions": [1, 1, 1]
-}

MC/config/PWGHF/ini/GeneratorHF_Non_Hfe.ini

@@ -1,7 +1,7 @@
-#### This configuration uses the Box generator to trigger π⁰/η production within the specified rapidity window
 [GeneratorExternal]
 fileName=${O2DPG_MC_CONFIG_ROOT}/MC/config/PWGHF/external/generator/selectNonHfe.C
-funcName = generatePythia8Box(0.1, 50.0)
+funcName=generatePythia8Box(0.1,50.0)
+
 [GeneratorPythia8]
 config=${O2DPG_MC_CONFIG_ROOT}/MC/config/PWGHF/pythia8/generator/pythia8_NonHfe.cfg
-includePartonEvent=true
+includePartonEvent=true

MC/config/PWGHF/pythia8/generator/pythia8_NonHfe.cfg

@@ -9,8 +9,8 @@ Beams:eCM 13600. 		# GeV
 
 ### processes
 
-ProcessLevel:all = off     
 
+SoftQCD:inelastic  = on       
 ### decays
 ParticleDecays:limitTau0 on	
 ParticleDecays:tau0Max 10.