Simplify parameterized single mu generator (#1898)

* Single mu generator: fix file naming, configurable pdg

* Simplify parameterized single mu generator

* Remove unused fields

Author: nburmaso

MC/config/PWGDQ/external/generator/GeneratorParamMuon.C

@@ -0,0 +1,161 @@
+// Parameterized generator for muons
+// Adaptation of the Run 2 generator by P. Pillot:
+// https://github.com/alisw/AliDPG/blob/master/MC/CustomGenerators/PWGDQ/Muon_GenParamSingle_PbPb5TeV_1.C
+
+#include "FairGenerator.h"
+#include "TF1.h"
+#include "TRandom.h"
+#include "TDatabasePDG.h"
+#include "TParticlePDG.h"
+
+class O2_GeneratorParamMuon : public FairGenerator
+{
+ public:
+  O2_GeneratorParamMuon(int npart = 2, int pdg = 13, double ymin = -4.3, double ymax = -2.3, double ptmin = 0.1, double ptmax = 999.)
+    : FairGenerator("ParaMuon"), fNParticles(npart), fPDGCode(pdg), fYMin(ymin), fYMax(ymax), fPtMin(ptmin), fPtMax(ptmax)
+  {
+    TParticlePDG* particle = TDatabasePDG::Instance()->GetParticle(fPDGCode);
+    fMass = particle->Mass();
+    fMass2 = fMass * fMass;
+  }
+
+  ~O2_GeneratorParamMuon() = default;
+
+  void SetRandomCharge(bool flag) { fRandomizeCharge = flag; }
+
+  void SetPtPars(double p0, double p1, double p2, double p3, double p4, double p5)
+  {
+    fPtP0 = p0;
+    fPtP1 = p1;
+    fPtP2 = p2;
+    fPtP3 = p3;
+    fPtP4 = p4;
+    fPtP5 = p5;
+  }
+
+  void SetYPars(double p0, double p1, double p2, double p3, double p4)
+  {
+    fYP0 = p0;
+    fYP1 = p1;
+    fYP2 = p2;
+    fYP3 = p3;
+    fYP4 = p4;
+  }
+
+  void InitParaFuncs()
+  {
+    fPtPara = new TF1("pt-para", PtMuon, fPtMin, fPtMax, 6);
+    fPtPara->SetParameter(0, fPtP0);
+    fPtPara->SetParameter(1, fPtP1);
+    fPtPara->SetParameter(2, fPtP2);
+    fPtPara->SetParameter(3, fPtP3);
+    fPtPara->SetParameter(4, fPtP4);
+    fPtPara->SetParameter(5, fPtP5);
+    fYPara = new TF1("y-para", YMuon, fYMin, fYMax, 5);
+    fYPara->SetParameter(0, fYP0);
+    fYPara->SetParameter(1, fYP1);
+    fYPara->SetParameter(2, fYP2);
+    fYPara->SetParameter(3, fYP3);
+    fYPara->SetParameter(4, fYP4);
+  }
+
+  static double PtMuon(const double* xx, const double* par)
+  {
+    double x = xx[0];
+    double p0 = par[0];
+    double p1 = par[1];
+    double p2 = par[2];
+    double p3 = par[3];
+    double p4 = par[4];
+    double p5 = par[5];
+    return p0 * (1. / std::pow(p1 + std::pow(x, p2), p3) + p4 * std::exp(p5 * x));
+  }
+
+  static double YMuon(const double* xx, const double* par)
+  {
+    double x = xx[0];
+    double p0 = par[0];
+    double p1 = par[1];
+    double p2 = par[2];
+    double p3 = par[3];
+    double p4 = par[4];
+    double x2 = x * x;
+    return p0 * (1. + p1 * x + p2 * x2 + p3 * x2 * x + p4 * x2 * x2);
+  }
+
+  bool ReadEvent(FairPrimaryGenerator* primGen) override
+  {
+    // no kinematic cuts -> accepting all
+    for (int i = 0; i < fNParticles; ++i) {
+      double pt = fPtPara->GetRandom();
+      double ty = std::tanh(fYPara->GetRandom());
+      double xmt = std::sqrt(pt * pt + fMass2);
+      double pl = xmt * ty / std::sqrt((1. - ty * ty));
+      double phi = gRandom->Uniform(0., 2. * M_PI);
+      double px = pt * std::cos(phi);
+      double py = pt * std::sin(phi);
+      int pdg = fPDGCode;
+      if (fRandomizeCharge) {
+        int charge;
+        if (gRandom->Rndm() < 0.5) {
+          charge = 1;
+        } else {
+          charge = -1;
+        }
+        pdg = std::abs(pdg) * charge;
+      }
+      primGen->AddTrack(pdg, px, py, pl, 0, 0, 0);
+      printf("Add track %d %.2f %.2f %.2f  \n", pdg, px, py, pl);
+    }
+    return kTRUE;
+  }
+
+ private:
+  TF1* fPtPara{nullptr};
+  TF1* fYPara{nullptr};
+  TF1* fdNdPhi{nullptr};
+
+  // parameters tuned to Pb-Pb @ 5.02 TeV
+  double fPtP0{797.446};
+  double fPtP1{0.830278};
+  double fPtP2{0.632177};
+  double fPtP3{10.2202};
+  double fPtP4{-0.000614809};
+  double fPtP5{-1.70993};
+
+  double fYP0{1.87732};
+  double fYP1{0.00658212};
+  double fYP2{-0.0988071};
+  double fYP3{-0.000452746};
+  double fYP4{0.00269782};
+
+  // configuration
+  int fPDGCode{13};
+  int fNParticles{2};
+  double fYMin{-4.3};
+  double fYMax{-2.3};
+  double fPtMin{0.1};
+  double fPtMax{999.};
+  bool fRandomizeCharge{true};
+  double fMass{0.10566};
+  double fMass2{0};
+};
+
+FairGenerator* paramMuGen(double ptP0 = 797.446, double ptP1 = 0.830278,
+                          double ptP2 = 0.632177, double ptP3 = 10.2202,
+                          double ptP4 = -0.000614809, double ptP5 = -1.70993,
+                          double yP0 = 1.87732, double yP1 = 0.00658212,
+                          double yP2 = -0.0988071, double yP3 = -0.000452746,
+                          double yP4 = 0.00269782,
+                          int nPart = 2, int pdg = 13,
+                          double ymin = -4.3, double ymax = -2.3,
+                          double ptmin = 0.1, float ptmax = 999.,
+                          int randCharge = 1)
+{
+  auto* gen = new O2_GeneratorParamMuon(nPart, pdg, ymin, ymax, ptmin, ptmax);
+  gen->SetPtPars(ptP0, ptP1, ptP2, ptP3, ptP4, ptP5);
+  gen->SetYPars(yP0, yP1, yP2, yP3, yP4);
+  gen->InitParaFuncs();
+  gen->SetRandomCharge(randCharge);
+  return gen;
+}