Generators will tell its length/time units to AliGenMC for Boost method

AliGenMC::Boost() method assumes m/s for length/time units. In case the generator
uses other units it must set the AliGenMC::SetGeneratorUnitsForMeterSecond(lgtC, timeC)
with lgtC and timeC being the coefficients translating generator's units to m/s.

Author: shahor02

EVGEN/AliGenMC.cxx

@@ -33,6 +33,7 @@
 #include "AliRun.h"
 #include "AliGeometry.h"
 #include "AliDecayer.h"
+#include "AliLog.h"
 
 ClassImp(AliGenMC)
 
@@ -57,6 +58,8 @@ AliGenMC::AliGenMC()
      fForceDecay(kAll),
      fMaxLifeTime(1.e-15),
      fDyBoost(0.),
+     fSpace2TimeCoeff(1.),
+     fTime2SpaceCoeff(1.),
      fGeometryAcceptance(0),
      fPdgCodeParticleforAcceptanceCut(0),
      fNumberOfAcceptedParticles(0),
@@ -92,6 +95,8 @@ AliGenMC::AliGenMC(Int_t npart)
      fForceDecay(kAll),
      fMaxLifeTime(1.e-15),
      fDyBoost(0.),
+     fSpace2TimeCoeff(1.),
+     fTime2SpaceCoeff(1.),
      fGeometryAcceptance(0),
      fPdgCodeParticleforAcceptanceCut(0),
      fNumberOfAcceptedParticles(0),
@@ -426,8 +431,8 @@ void AliGenMC::Boost()
 	Double_t vy  = iparticle->Vy();
 	Double_t vz  = iparticle->Vz();
 
-	Double_t ctb = gamma * ct -      gb * vz;
-	Double_t vzb =   -gb * ct +   gamma * vz;
+	Double_t ctb = gamma * ct -      gb * vz * fSpace2TimeCoeff;
+	Double_t vzb =   -gb * ct * fTime2SpaceCoeff +   gamma * vz;
 
 	iparticle->SetProductionVertex(vx, vy, vzb, ctb * c_1);
     }
@@ -482,3 +487,15 @@ void AliGenMC::AddHeader(AliGenEventHeader* header)
       if (gAlice) gAlice->SetGenEventHeader(header);	
     }
 }
+
+void AliGenMC::SetGeneratorUnitsForMeterSecond(double lengthC, double timeC)
+{
+  // set scaling coeffs to convert length and time units used by generator to
+  // m and s. We store only their ratio, relevant for the Boost
+  if (timeC<1e-30 || lengthC<1e-30) {
+    AliFatal("Provided lenght and time units must be positive");
+  }
+  AliInfoF("Boost will scale length by %e and time by %e to obtain meter and second",lengthC,timeC);
+  fSpace2TimeCoeff = lengthC/timeC;
+  fTime2SpaceCoeff = timeC/lengthC;
+}

EVGEN/AliGenMC.h

@@ -63,6 +63,8 @@ class AliGenMC : public AliGenerator
     virtual void BeamCrossAngle();
     virtual void AddHeader(AliGenEventHeader* header);
 
+    virtual void SetGeneratorUnitsForMeterSecond(double lengthC=1., double timeC=1.);
+    
  protected:
     // check if particle is selected as parent particle
     Bool_t ParentSelected(Int_t ip) const;
@@ -92,16 +94,18 @@ class AliGenMC : public AliGenerator
     Decay_t      fForceDecay;    // Decay channel forced
     Float_t      fMaxLifeTime;   // Maximum lifetime for unstable particles
     Double_t     fDyBoost;       // dy for boost into lab frame
+    Double_t     fSpace2TimeCoeff;            // coeff to convert lenght/time units used by generator to m/s
+    Double_t     fTime2SpaceCoeff;            // coeff to convert time/length units used by generator to s/m
     AliGeometry* fGeometryAcceptance; // Geometry to which particles must be simulated
     Int_t        fPdgCodeParticleforAcceptanceCut;  // Abs(PDG Code) of the particle to which the GeometryAcceptance must be applied
     Int_t        fNumberOfAcceptedParticles;  // Number of accepted particles in GeometryAcceptance with the right Abs(PdgCode) 
     Int_t        fNprimaries;                 // Number of produced and stored particles
- 
+    
  private:
     AliGenMC(const AliGenMC &MC);
     AliGenMC & operator=(const AliGenMC & rhs);
 
-    ClassDef(AliGenMC,7)       // AliGenerator implementation for generators using MC methods
+    ClassDef(AliGenMC,8)       // AliGenerator implementation for generators using MC methods
 };
 #endif
 

PYTHIA6/AliPythia6/AliGenPythia.cxx

@@ -394,7 +394,10 @@ void AliGenPythia::SetEventListRange(Int_t eventFirst, Int_t eventLast)
 void AliGenPythia::Init()
 {
 // Initialisation
-    
+
+    // Coeffs to go from mm / mm to meter / second
+    SetGeneratorUnitsForMeterSecond(1.e-3, 1e-3/TMath::C()); 
+  
     SetMC(AliPythia::Instance());
     fPythia=(AliPythia*) fMCEvGen;
 

PYTHIA6/AliPythia6/AliGenPythiaPlus.cxx

@@ -328,7 +328,10 @@ void AliGenPythiaPlus::Init()
 
 //    SetMC(AliPythia::Instance());
 //    fPythia=(AliPythia*) fMCEvGen;
-    
+  
+    // Coeffs to go from mm / mm to meter / second
+    SetGeneratorUnitsForMeterSecond(1.e-3, 1e-3/TMath::C()); 
+  
 //
     fParentWeight=1./Float_t(fNpart);
 //

TAmpt/TAmpt/AliGenAmpt.cxx

@@ -161,6 +161,9 @@ void AliGenAmpt::Init()
 {
   // Initialisation
 
+  // Coeffs to go to from cm/s to meter/seconds
+  SetGeneratorUnitsForMeterSecond(1.e-2, 1.); 
+  
   fFrame.Resize(8);
   fTarget.Resize(8);
   fProjectile.Resize(8);

TDPMjet/AliGenDPMjet.cxx

@@ -176,7 +176,10 @@ AliGenDPMjet::~AliGenDPMjet()
 void AliGenDPMjet::Init()
 {
 // Initialization
-    
+
+    // Coeffs to go from mm / mm to meter / second
+    SetGeneratorUnitsForMeterSecond(1.e-3, 1e-3/TMath::C()); 
+  
     if(fEnergyCMS>0. && fBeamEn<0.1) fBeamEn = fEnergyCMS/2;
     SetMC(new TDPMjet(fProcess, fAProjectile, fZProjectile, fATarget, fZTarget, 
 		      fBeamEn,fEnergyCMS));

THijing/AliGenHijing.cxx

@@ -166,6 +166,10 @@ AliGenHijing::~AliGenHijing()
 void AliGenHijing::Init()
 {
 // Initialisation
+
+    // Coeffs to go from mm / mm to meter / second
+    SetGeneratorUnitsForMeterSecond(1.e-3, 1e-3/TMath::C()); 
+  
     fFrame.Resize(8);
     fTarget.Resize(8);
     fProjectile.Resize(8);