Simulation example of embedding of adaptive Pythia8 signals

Author: preghenella

MC/config/examples/external/generator/adaptive_pythia8.C

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+/// \author R+Preghenella - April 2020
+
+// Example of an implementation of an external event generator
+// that is used and adapts it behavior in an embedding scenario.
+//
+//   usage: o2sim -g external --configKeyValues 'GeneratorExternal.fileName=adaptive_pythia8.C;GeneratorExternal.funcName="adaptive_pythia8(\"0.001 * x\")"'
+
+using namespace o2::eventgen;
+
+class Adaptive_Pythia8 : public GeneratorPythia8
+{
+public:
+  Adaptive_Pythia8(const char *formula = "0.01 * x") :
+    GeneratorPythia8(), mFormula("formula", formula) { };
+  ~Adaptive_Pythia8() = default;
+
+  // update the number of events to be generated
+  // according to background primaries and formula
+  void notifyEmbedding(const FairMCEventHeader *bkgHeader) override {
+    auto nPrimaries = bkgHeader->GetNPrim();
+    mEvents = mFormula.Eval(nPrimaries);
+  };
+  
+  // generate event and import particles
+  // multiple times according to background and formula
+  Bool_t generateEvent() override {
+    for (int iev = 0; iev < mEvents; ++iev) {
+      if (!GeneratorPythia8::generateEvent()) return false;
+      if (!GeneratorPythia8::importParticles()) return false;
+    }
+    return true; };
+
+  // override this function to avoid importing particles
+  // of the last event again as this is called by the base class
+  Bool_t importParticles() override { return true; }
+
+private:
+
+  int mEvents = 1;
+  TFormula mFormula;
+  
+};
+
+FairGenerator*
+adaptive_pythia8(const char *formula = "0.01 * x")
+{
+  std::cout << " --- adaptive_pythia8 initialising with formula: " << formula << std::endl;
+  auto py8 = new Adaptive_Pythia8(formula);
+  return py8;
+}

MC/config/examples/ini/adaptive_pythia8.ini

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+### The setup uses an external even generator which is configured
+### to generate as many Pythia8 events according to a formula
+### The formula is passed via the function call, where x if the
+### number of primary particles in the background event
+
+[GeneratorExternal]
+fileName=${O2DPG_ROOT}/MC/config/examples/external/generator/adaptive_pythia8.C
+funcName=adaptive_pythia8("0.002 * x")
+
+### The external generator derives from GeneratorPythia8.
+### This part configures the underlying Pythia8 configuration.
+
+[GeneratorPythia8]
+config = ${O2DPG_ROOT}/MC/config/common/pythia8/generator/pythia8_inel.cfg

MC/run/examples/adaptive_pythia8.sh

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+#!/usr/bin/env bash
+
+### This script run the simulation of signal embedding into a heavy-ion background.
+### First the background is generated with Pythia8/Angantyr model and basic settings.
+### The signal generation is configured to be embedded into the background (--embedIntoFile).
+### The signal event generator is an external event generator which implements adaptive
+### features where the number of events to be injected depends on the characteristics
+### of the background.
+### The details are defined in the INI config files (--configFile).
+
+set -x
+
+MODULES="PIPE ITS TPC"
+BKGEVENTS=5
+SIGEVENTS=20
+NWORKERS=8
+
+# generate background
+
+o2-sim -j ${NWORKERS} -n ${BKGEVENTS} -g pythia8hi -m ${MODULES} -o bkg \
+       --configFile ${O2DPG_ROOT}/MC/config/common/ini/basic.ini \
+       > logbkg 2>&1
+
+# embed signal into background
+
+o2-sim -j ${NWORKERS} -n ${SIGEVENTS} -g external -m ${MODULES} -o sgn \
+       --configFile ${O2DPG_ROOT}/MC/config/examples/ini/adaptive_pythia8.ini \
+       --embedIntoFile bkg_Kine.root \
+       > logsgn 2>&1