G4LorentzConvertor.cc

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// $Id: G4LorentzConvertor.cc 66241 2012-12-13 18:34:42Z gunter $
//
// 20100108  Michael Kelsey -- Use G4LorentzVector internally
// 20100112  M. Kelsey -- Remove G4CascadeMomentum, use G4LorentzVector directly
// 20100308  M. Kelsey -- Bug fix in toTheTargetRestFrame: scm_momentum should
//              be data member, not local.
// 20100409  M. Kelsey -- Protect std::sqrt(ga) against round-off negatives
// 20100519  M. Kelsey -- Add interfaces to pass G4InuclParticles directly
// 20100617  M. Kelsey -- Add more diagnostic messages with multiple levels
// 20100713  M. Kelsey -- All diagnostic messages should be verbose > 1
// 20110525  M. Kelsey -- Add some diagnostic messages in both ::rotate()
// 20110602  M. Kelsey -- Simplify some kinematics, dropping intermediate calcs

#include "G4LorentzConvertor.hh"
#include "G4ThreeVector.hh"
#include "G4HadronicException.hh"
#include "G4InuclParticle.hh"


const G4double G4LorentzConvertor::small = 1.0e-10;

G4LorentzConvertor::G4LorentzConvertor() 
  : verboseLevel(0), v2(0.), ecm_tot(0.), valong(0.), degenerated(false) {}

G4LorentzConvertor::
G4LorentzConvertor(const G4LorentzVector& bmom, G4double bmass, 
                   const G4LorentzVector& tmom, G4double tmass) 
  : verboseLevel(0), v2(0.), ecm_tot(0.), valong(0.), degenerated(false) {
  setBullet(bmom, bmass);
  setTarget(tmom, tmass);
}

G4LorentzConvertor::
G4LorentzConvertor(const G4InuclParticle* bullet, 
                   const G4InuclParticle* target) 
  : verboseLevel(0), v2(0.), ecm_tot(0.), valong(0.), degenerated(false) {
  setBullet(bullet);
  setTarget(target);
}

// Extract four-vectors from input particles
void G4LorentzConvertor::setBullet(const G4InuclParticle* bullet) {
  setBullet(bullet->getMomentum());
}

void G4LorentzConvertor::setTarget(const G4InuclParticle* target) {
  setTarget(target->getMomentum());
}


// Boost bullet and target four-vectors into desired frame

void G4LorentzConvertor::toTheCenterOfMass() {
  if (verboseLevel > 2)
    G4cout << " >>> G4LorentzConvertor::toTheCenterOfMass" << G4endl;

  velocity = (target_mom+bullet_mom).boostVector();
  if (verboseLevel > 3) G4cout << " boost " << velocity << G4endl;

  // "SCM" is reverse target momentum in the CM frame
  scm_momentum = target_mom;
  scm_momentum.boost(-velocity);
  scm_momentum.setVect(-scm_momentum.vect());

  if (verboseLevel > 3) G4cout << " pscm " << scm_momentum.vect() << G4endl;

  fillKinematics();
}

void G4LorentzConvertor::toTheTargetRestFrame() {
  if (verboseLevel > 2)
    G4cout << " >>> G4LorentzConvertor::toTheTargetRestFrame" << G4endl;

  velocity = target_mom.boostVector();
  if (verboseLevel > 3) G4cout << " boost " << velocity << G4endl;

  // "SCM" is bullet momentum in the target's frame
  scm_momentum = bullet_mom;
  scm_momentum.boost(-velocity);

  if (verboseLevel > 3) G4cout << " pseudo-pscm " << scm_momentum.vect() << G4endl;

  fillKinematics();
}

// Compute kinematic quantities for rotate() functions

void G4LorentzConvertor::fillKinematics() {
  ecm_tot = (target_mom+bullet_mom).m();

  scm_direction = scm_momentum.vect().unit();
  valong = velocity.dot(scm_direction);

  v2 = velocity.mag2();

  G4double pvsq = v2 - valong*valong;           // velocity perp to scm_momentum
  if (verboseLevel > 3) G4cout << " pvsq " << pvsq << G4endl;

  degenerated = (pvsq < small);
  if (degenerated && verboseLevel > 2) 
    G4cout << " degenerated case (already along Z) " << G4endl; 

  if (verboseLevel > 3) {
    G4cout << " v2 " << v2 << " valong " << valong
           << " valong*valong " << valong*valong << G4endl;
  }
}

G4LorentzVector 
G4LorentzConvertor::backToTheLab(const G4LorentzVector& mom) const {
  if (verboseLevel > 2)
    G4cout << " >>> G4LorentzConvertor::backToTheLab" << G4endl;

  if (verboseLevel > 3)
    G4cout << " at rest: px " << mom.x() << " py " << mom.y() << " pz "
           << mom.z() << " e " << mom.e() << G4endl
           << " v2 " << v2 << G4endl;

  G4LorentzVector mom1 = mom;
  if (v2 > small) mom1.boost(velocity);

  if (verboseLevel > 3)
    G4cout << " at lab: px " << mom1.x() << " py " << mom1.y() << " pz "
           << mom1.z() << G4endl;

  return mom1;
}


// Bullet kinematics in target rest frame (LAB frame, usually)

G4double G4LorentzConvertor::getKinEnergyInTheTRS() const {
  if (verboseLevel > 2)
    G4cout << " >>> G4LorentzConvertor::getKinEnergyInTheTRS" << G4endl;

  G4LorentzVector bmom = bullet_mom;
  bmom.boost(-target_mom.boostVector());
  return bmom.e()-bmom.m();
}

G4double G4LorentzConvertor::getTRSMomentum() const {
  if (verboseLevel > 2)
    G4cout << " >>> G4LorentzConvertor::getTRSMomentum" << G4endl;

  G4LorentzVector bmom = bullet_mom;
  bmom.boost(-target_mom.boostVector());
  return bmom.rho();
}

G4LorentzVector G4LorentzConvertor::rotate(const G4LorentzVector& mom) const {
  if (verboseLevel > 2)
    G4cout << " >>> G4LorentzConvertor::rotate(G4LorentzVector)" << G4endl;

  if (verboseLevel > 3) {
    G4cout << " valong " << valong << " degenerated " << degenerated << G4endl
           << " before rotation: px " << mom.x() << " py " << mom.y()
           << " pz " << mom.z() << G4endl;
  }

  G4LorentzVector mom_rot = mom;
  if (!degenerated) {
    if (verboseLevel > 2)
      G4cout << " rotating to align with reference z axis " << G4endl;

    G4ThreeVector vscm = velocity - valong*scm_direction;
    G4ThreeVector vxcm = scm_direction.cross(velocity);

    if (vscm.mag() > small && vxcm.mag() > small) {     // Double check
      if (verboseLevel > 3) {
        G4cout << " reference z axis " << scm_direction
               << " vscm " << vscm << " vxcm " << vxcm << G4endl;
      }
      
      mom_rot.setVect(mom.x()*vscm.unit() + mom.y()*vxcm.unit() +
                      mom.z()*scm_direction);
    } else {
      if (verboseLevel) 
        G4cerr << ">>> G4LorentzVector::rotate zero with !degenerated" << G4endl;
    }
  }

  if (verboseLevel > 3) {
    G4cout << " after rotation: px " << mom_rot.x() << " py " << mom_rot.y()
           << " pz " << mom_rot.z() << G4endl;
  }

  return mom_rot;
}

G4LorentzVector G4LorentzConvertor::rotate(const G4LorentzVector& mom1, 
                                           const G4LorentzVector& mom) const {
  if (verboseLevel > 2)
    G4cout << " >>> G4LorentzConvertor::rotate(G4LorentzVector,G4LorentzVector)"
           << G4endl;

  if (verboseLevel > 3) {
    G4cout << " before rotation: px " << mom.x() << " py " << mom.y()
           << " pz " << mom.z() << G4endl;
  }

  G4ThreeVector mom1_dir = mom1.vect().unit();
  G4double pv = velocity.dot(mom1_dir);

  G4double vperp = v2 - pv*pv;          // velocity perpendicular to mom1
  if (verboseLevel > 3) {
    G4cout << " vperp " << vperp << " small? " << (vperp <= small) << G4endl;
  }

  G4LorentzVector mom_rot = mom;

  if (vperp > small) {
    if (verboseLevel > 2)
      G4cout << " rotating to align with first z axis " << G4endl;

    G4ThreeVector vmom1 = velocity - pv*mom1_dir;
    G4ThreeVector vxm1  = mom1_dir.cross(velocity);

    if (vmom1.mag() > small && vxm1.mag() > small) {    // Double check
      if (verboseLevel > 3) {
        G4cout << " first z axis " << mom1_dir << G4endl
               << " vmom1 " << vmom1 << " vxm1 " << vxm1 << G4endl;
      }
      
      mom_rot.setVect(mom.x()*vmom1.unit() + mom.y()*vxm1.unit() +
                      mom.z()*mom1_dir );
    } else {
      if (verboseLevel) 
        G4cerr << ">>> G4LorentzVector::rotate zero with !degenerated" << G4endl;
    }
  }

  if (verboseLevel > 3) {
    G4cout << " after rotation: px " << mom_rot.x() << " py " << mom_rot.y()
           << " pz " << mom_rot.z() << G4endl;
  }

  return mom_rot;
}

G4bool G4LorentzConvertor::reflectionNeeded() const {
  if (verboseLevel > 2)
    G4cout << " >>> G4LorentzConvertor::reflectionNeeded (query)" << G4endl;

  if (verboseLevel > 3) {
    G4cout << " v2 = " << v2 << " SCM z = " << scm_momentum.z()
           << " degenerated? " << degenerated << G4endl;
  }

  if (v2 < small && !degenerated) 
    throw G4HadronicException(__FILE__, __LINE__, "G4LorentzConvertor::reflectionNeeded - return value undefined");

  if (verboseLevel > 2) {
    G4cout << " reflection across XY is"
           << ((v2>=small && (!degenerated || scm_momentum.z()<0.0))?"":" NOT")
           << " needed" << G4endl;
  }

  return (v2>=small && (!degenerated || scm_momentum.z()<0.0));
}


// Reporting functions for diagnostics

void G4LorentzConvertor::printBullet() const {
  G4cout << " G4LC bullet: px " << bullet_mom.px() << " py " << bullet_mom.py()
         << " pz " << bullet_mom.pz() << " e " << bullet_mom.e()
         << " mass " << bullet_mom.m() << G4endl;
  }

void G4LorentzConvertor::printTarget() const {
  G4cout << " G4LC target: px " << target_mom.px() << " py " << target_mom.py()
         << " pz " << target_mom.pz() << " e " << target_mom.e()
         << " mass " << target_mom.m() << G4endl;
}