G4bool CheckVolumeSD::ProcessHits(G4Step* aStep, G4TouchableHistory*)
{
  const G4Track* track = aStep->GetTrack();
  if (track->GetDefinition()->GetParticleName() == "gamma") {
    e = track->GetKineticEnergy();
    G4ThreeVector m = track->GetMomentumDirection();
    //G4ThreeVector p = track->GetPosition();
    mx = m.x();
    my = m.y();
    mz = m.z();
    mm = sqrt(pow(mx,2)+pow(my,2)+pow(mz,2));
    angx = acos(mx/mm);
    angy = acos(my/mm);
    angz = acos(mz/mm);
    }
  
  return true;
}


The question I have is about the reference point for the Momentum Vector-
is it in relation to the interacting electron vector at the point of photon
generation or something else entirely?


Makoto Asai:
Position, momentum, etc. of a track is with respect to
the world reference system, i.e. axes of the world volume.