GeneratorKrDecay.h

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// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
// All rights not expressly granted are reserved.
//
// This software is distributed under the terms of the GNU General Public
// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
//
// In applying this license CERN does not waive the privileges and immunities
// granted to it by virtue of its status as an Intergovernmental Organization
// or submit itself to any jurisdiction.
 
 
#ifndef ALICEO2_TPC_GeneratorKrDecay_H_
#define ALICEO2_TPC_GeneratorKrDecay_H_
 
#include "Generators/Generator.h"
#include <array>
#include <memory>
#include <vector>
 
namespace o2::tpc
{
 
class KrDecayTable
{
 public:
  struct Product {
    int pdg;
    double eKin;
  };
  struct Channel {
    double fraction;
    int nProducts;
    Product products[6]; // max 5 used; 6 for safety
  };
  // Eight physically motivated channels (T1 mode x T2 mode):
  //   T1: ICC_total=2035 -> 99.951% IC (75.163% outer-shell, 24.788% K-shell), 0.049% gamma
  //       K-shell: 65.2% K-fluorescence (Kalpha), 34.8% K-Auger
  //   T2: ICC_total=17.09 -> 94.472% IC, 5.528% gamma
  //   Source: G4 PhotonEvaporation5.7/z36.a83, RadioactiveDecay5.6/z36.a83
  static const int kNChannels = 8;
  Channel channels[kNChannels];
  double cumulative[kNChannels];
  KrDecayTable();
  const Channel& sample() const;
 
 private:
  // Parse $G4LEVELGAMMADATA/z36.a83. Returns true and fills five values
  // (energies in keV) on success.
  static bool parseG4PhotonEvap(const char* path, double& E_T1, double& ICC_T1,
                                double& Kfrac_T1, double& E_T2, double& ICC_T2);
};
 
} // namespace o2::tpc
 
namespace o2::eventgen
{
 
class GeneratorKrDecay : public Generator
{
 public:
  GeneratorKrDecay();
  ~GeneratorKrDecay() override;
  Bool_t Init() override;
  Bool_t generateEvent() override;
  Bool_t importParticles() override;
 
 private:
  static constexpr double kRInner = 83.5;
  static constexpr double kROuter = 246.5; // TPC outermost pad row outer edge ~247 cm; stay inside
  static constexpr double kHalfZ = 249.7;
 
  // O2 status encoding from MCGenProperties.h
  // bits 0-8: hepmc(9), bits 9-18: gen(10), bits 19-28: reserved(10), bits 29-31: sentinel=5
  static int krO2EncodedStatus(int hepmc, int gen = 0);
 
  int mNPerEvent = 1000; // Kr decays per event; overridable at runtime via KR_N_PER_EVENT env var
  std::unique_ptr<o2::tpc::KrDecayTable> mTable;
  std::vector<std::array<double, 3>> mVertices;
  // No ClassDefOverride: the base Generator class's dictionary is sufficient
  // for a runtime-only generator that is never streamed via ROOT I/O
  // (matches o2::eventgen::GeneratorGeantinos and other Generator subclasses).
};
 
} // namespace o2::eventgen
 
#endif // ALICEO2_TPC_GeneratorKrDecay_H_