implement the rotation.

Generator/src/GtBeamBackgroundTool.cpp

 #include "GtBeamBackgroundTool.h"
 #include "IBeamBackgroundFileParser.h"
 #include "BeamBackgroundFileParserV0.h"
+
+#include "TVector3.h" // for rotation
 DECLARE_COMPONENT(GtBeamBackgroundTool)
 
 StatusCode GtBeamBackgroundTool::initialize() {
@@ -9,8 +11,17 @@ StatusCode GtBeamBackgroundTool::initialize() {
     // create the instances of the background parsers
 
     for (auto& [label, inputfn]: m_inputmaps) {
-        
-        m_beaminputs[label] = std::make_shared<BeamBackgroundFileParserV0>(inputfn, 11, 125.);
+        double beamE = 120.;
+        auto itBeamE = m_Ebeammaps.find(label);
+        if (itBeamE != m_Ebeammaps.end()) {
+            beamE = itBeamE->second;
+        }
+        info() << "Initializing beam background ... "
+               << label << " "
+               << beamE << " "
+               << inputfn
+               << endmsg;
+        m_beaminputs[label] = std::make_shared<BeamBackgroundFileParserV0>(inputfn, 11, beamE);
     }
 
     // check the size
@@ -43,6 +54,17 @@ bool GtBeamBackgroundTool::mutate(MyHepMC::GenEvent& event) {
         // fill the value
         float charge = beamdata.pdgid == 11 ? -1: 1;
 
+        TVector3 pos(beamdata.x,beamdata.y,beamdata.z);
+        TVector3 mom(beamdata.px,beamdata.py,beamdata.pz);
+
+        auto itrot = m_rotYmaps.find(label);
+        if (itrot  != m_rotYmaps.end() ) {
+            info() << "Apply rotation along Y " << itrot->second << endmsg;
+
+            pos.RotateY(itrot->second);
+            mom.RotateY(itrot->second);
+        }
+
         // create the MC particle
         edm4hep::MCParticle mcp = event.m_mc_vec.create();
         mcp.setPDG(beamdata.pdgid);
@@ -51,8 +73,8 @@ bool GtBeamBackgroundTool::mutate(MyHepMC::GenEvent& event) {
         mcp.setCharge(static_cast<float>(charge));
         mcp.setTime(beamdata.t);
         mcp.setMass(beamdata.mass);
-        mcp.setVertex(edm4hep::Vector3d(beamdata.x,beamdata.y,beamdata.z)); 
-        mcp.setMomentum(edm4hep::Vector3f(beamdata.px,beamdata.py,beamdata.pz));
+        mcp.setVertex(edm4hep::Vector3d(pos.X(), pos.Y(), pos.Z())); 
+        mcp.setMomentum(edm4hep::Vector3f(mom.X(), mom.Y(), mom.Z()));
 
     }
     

Generator/src/GtBeamBackgroundTool.h

@@ -51,6 +51,12 @@ private:
     Gaudi::Property<std::map<std::string, std::string>> m_fomatmaps{this, "InputFormatMap"};
     Gaudi::Property<std::map<std::string, double>>      m_ratemaps {this, "InputRateMap"};
 
+    // unit of beam energy: GeV
+    Gaudi::Property<std::map<std::string, double>>      m_Ebeammaps{this, "InputBeamEnergyMap"};
+
+    // unit of the rotation along Y: rad
+    Gaudi::Property<std::map<std::string, double>>      m_rotYmaps {this, "RotationAlongYMap"};
+
 private:
     std::map<std::string, std::shared_ptr<IBeamBackgroundFileParser>> m_beaminputs;