Include/adapt QED for special runs (AliceO2Group#14242)

* Include QED for special runs

Author: jackal1-66

Generators/include/Generators/QEDGenParam.h

@@ -24,11 +24,12 @@ namespace o2
 namespace eventgen
 {
 struct QEDGenParam : public o2::conf::ConfigurableParamHelper<QEDGenParam> {
-
-  float yMin = -6.f;    ///< min Y
-  float yMax = 6.f;     ///< max Y
-  float ptMin = 0.4e-3; ///< min pT
-  float ptMax = 10.f;   ///< min pT
+  float yMin = -6.f;       ///< min Y
+  float yMax = 6.f;        ///< max Y
+  float ptMin = 0.4e-3;    ///< min pT
+  float ptMax = 10.f;      ///< min pT
+  float cmEnergy = 5360.f; ///< center of mass energy per nucleon pair in GeV
+  float Z = 82.f;          ///< atomic number of the projectile/target (only symmetric systems are compatible for now)
   //
   float xSectionQED = -1; ///< estimated QED x-section in barns
   float xSectionHad = 8.; ///< reference hadronic x-section for the same system

Generators/share/external/QEDepem.C

@@ -35,6 +35,8 @@ o2::eventgen::GeneratorTGenerator* QEDepem()
     genBg->SetPtRange(qedParam.ptMin, qedParam.ptMax);                               // Set pt limits (GeV) for e+-: 1MeV corresponds to max R=13.3mm at 5kGaus
     genBg->SetOrigin(diamond.position[0], diamond.position[1], diamond.position[2]); // vertex position in space
     genBg->SetSigma(diamond.width[0], diamond.width[1], diamond.width[2]);           // vertex sigma
+    genBg->SetCMEnergy(qedParam.cmEnergy);                                           // center of mass energy per nucleon pair in GeV
+    genBg->SetZ(qedParam.Z);                                                         // atomic number of the projectile/target (only symmetric systems are compatible for now)
     genBg->SetTimeOrigin(0.);                                                        // vertex position in time
     initialized = genBg->Init();
     if (!initialized) {