ClosestApproachInRPhi Class Reference

#include <ClosestApproachInRPhi.h>

Inheritance diagram for ClosestApproachInRPhi:

Public Member Functions
virtual bool	calculate (const TrajectoryStateOnSurface &sta, const TrajectoryStateOnSurface &stb)
virtual bool	calculate (const FreeTrajectoryState &sta, const FreeTrajectoryState &stb)
virtual ClosestApproachInRPhi *	clone () const
	ClosestApproachInRPhi ()
virtual GlobalPoint	crossingPoint () const
virtual float	distance () const
virtual std::pair< GlobalPoint, GlobalPoint >	points () const
virtual bool	status () const
std::pair < GlobalTrajectoryParameters, GlobalTrajectoryParameters >	trajectoryParameters () const
Public Member Functions inherited from ClosestApproachOnHelices
	ClosestApproachOnHelices ()
virtual	~ClosestApproachOnHelices ()

Private Member Functions
bool	compute (const TrackCharge &chargeA, const GlobalVector &momentumA, const GlobalPoint &positionA, const TrackCharge &chargeB, const GlobalVector &momentumB, const GlobalPoint &positionB)

Static Private Member Functions
static void	circleParameters (const TrackCharge &charge, const GlobalVector &momemtum, const GlobalPoint &position, double &xc, double &yc, double &r, double bz)
static GlobalTrajectoryParameters	newTrajectory (const GlobalPoint &newpt, const GlobalTrajectoryParameters &oldpar, double bz)
static int	transverseCoord (double cxa, double cya, double ra, double cxb, double cyb, double rb, double &xg1, double &yg1, double &xg2, double &yg2)
static double	zCoord (const GlobalVector &mom, const GlobalPoint &pos, double r, double xc, double yc, double xg, double yg)

Private Attributes
double	bz
GlobalTrajectoryParameters	paramA
GlobalTrajectoryParameters	paramB
GlobalPoint	posA
GlobalPoint	posB
bool	status_

Detailed Description

Given two trajectory states, computes the two points of closest approach in the transverse plane for the helices extrapolated from these states. 1) computes the intersections of the circles in transverse plane. Two cases: - circles have one or two intersection points;

• circles do not cross; the points used are the points of closest approach of the two circles. 2) computes the corresponding z-coordinates. In the case where the circles have two intersections, the point for which the z-coordinates on the 2 tracks are the closest is chosen.

Definition at line 18 of file ClosestApproachInRPhi.h.

Constructor & Destructor Documentation

ClosestApproachInRPhi::ClosestApproachInRPhi ( )

inline

Definition at line 22 of file ClosestApproachInRPhi.h.

References status_.

Referenced by clone().

{status_ = false;}

Member Function Documentation

bool ClosestApproachInRPhi::calculate ( const TrajectoryStateOnSurface &  sta, const TrajectoryStateOnSurface &  stb  )

virtual

Implements ClosestApproachOnHelices.

Definition at line 8 of file ClosestApproachInRPhi.cc.

References TrajectoryStateOnSurface::charge(), bookConverter::compute(), TrajectoryStateOnSurface::freeState(), TrajectoryStateOnSurface::globalMomentum(), TrajectoryStateOnSurface::globalParameters(), TrajectoryStateOnSurface::globalPosition(), MagneticField::inTesla(), GlobalTrajectoryParameters::magneticField(), FreeTrajectoryState::parameters(), and PV3DBase< T, PVType, FrameType >::z().

Referenced by HLTMuon::analyze(), NuclearVertexBuilder::closestApproach(), V0Fitter::fitAll(), HLTMuonTrackMassFilter::hltFilter(), HLTMuonTrimuonL3Filter::hltFilter(), HLTMuonDimuonL3Filter::hltFilter(), ConversionProducer::preselectTrackPair(), and cms::HITrackVertexMaker::produceTracks().

{
  TrackCharge chargeA = sta.charge(); TrackCharge chargeB = stb.charge();
  GlobalVector momentumA = sta.globalMomentum();
  GlobalVector momentumB = stb.globalMomentum();
  GlobalPoint positionA = sta.globalPosition();
  GlobalPoint positionB = stb.globalPosition();
  paramA = sta.globalParameters();
  paramB = stb.globalParameters();
  // compute magnetic field ONCE 
  bz = sta.freeState()->parameters().magneticField().inTesla(positionA).z() * 2.99792458e-3;

  return compute(chargeA, momentumA, positionA, chargeB, momentumB, positionB);

}

bool ClosestApproachInRPhi::calculate ( const FreeTrajectoryState &  sta, const FreeTrajectoryState &  stb  )

virtual

Implements ClosestApproachOnHelices.

Definition at line 26 of file ClosestApproachInRPhi.cc.

References FreeTrajectoryState::charge(), bookConverter::compute(), MagneticField::inTesla(), GlobalTrajectoryParameters::magneticField(), FreeTrajectoryState::momentum(), FreeTrajectoryState::parameters(), FreeTrajectoryState::position(), and PV3DBase< T, PVType, FrameType >::z().

{
  TrackCharge chargeA = sta.charge(); TrackCharge chargeB = stb.charge();
  GlobalVector momentumA = sta.momentum();
  GlobalVector momentumB = stb.momentum();
  GlobalPoint positionA = sta.position();
  GlobalPoint positionB = stb.position();
  paramA = sta.parameters();
  paramB = stb.parameters();
  // compute magnetic field ONCE 
  bz = sta.parameters().magneticField().inTesla(positionA).z() * 2.99792458e-3;

  return compute(chargeA, momentumA, positionA, chargeB, momentumB, positionB);

}

void ClosestApproachInRPhi::circleParameters ( const TrackCharge &  charge, const GlobalVector &  momemtum, const GlobalPoint &  position, double &  xc, double &  yc, double &  r, double  bz  )

staticprivate

temporary code, to be replaced by call to curvature() when bug is fixed.

end of temporary code

Definition at line 174 of file ClosestApproachInRPhi.cc.

References abs, PV3DBase< T, PVType, FrameType >::transverse(), PV3DBase< T, PVType, FrameType >::x(), and PV3DBase< T, PVType, FrameType >::y().

{

  // compute radius of circle
//   double bz = MagneticField::inInverseGeV(position).z();

  // signed_r directed towards circle center, along F_Lorentz = q*v X B
  double qob = charge/bz;
  double signed_r = qob*momentum.transverse();
  r = abs(signed_r);
  // compute centre of circle
  // double phi = momentum.phi();
  // xc = signed_r*sin(phi) + position.x();
  // yc = -signed_r*cos(phi) + position.y();
  xc =  position.x() + qob * momentum.y();
  yc =  position.y() - qob * momentum.x();

}

virtual ClosestApproachInRPhi* ClosestApproachInRPhi::clone ( void  ) const

inlinevirtual

Clone method

Implements ClosestApproachOnHelices.

Definition at line 51 of file ClosestApproachInRPhi.h.

References ClosestApproachInRPhi().

                                                {
    return new ClosestApproachInRPhi(* this);
  }

bool ClosestApproachInRPhi::compute ( const TrackCharge &  chargeA, const GlobalVector &  momentumA, const GlobalPoint &  positionA, const TrackCharge &  chargeB, const GlobalVector &  momentumB, const GlobalPoint &  positionB  )

private

Definition at line 69 of file ClosestApproachInRPhi.cc.

References abs.

{


  // centres and radii of track circles
  double xca, yca, ra;
  circleParameters(chargeA, momentumA, positionA, xca, yca, ra, bz);
  double xcb, ycb, rb;
  circleParameters(chargeB, momentumB, positionB, xcb, ycb, rb, bz);

  // points of closest approach in transverse plane
  double xg1, yg1, xg2, yg2;
  int flag = transverseCoord(xca, yca, ra, xcb, ycb, rb, xg1, yg1, xg2, yg2);
  if (flag == 0) {
    status_ = false;
    return false;
  }

  double xga, yga, zga, xgb, ygb, zgb;

  if (flag == 1) {
    // two crossing points on each track in transverse plane
    // select point for which z-coordinates on the 2 tracks are the closest
    double za1 = zCoord(momentumA, positionA, ra, xca, yca, xg1, yg1);
    double zb1 = zCoord(momentumB, positionB, rb, xcb, ycb, xg1, yg1);
    double za2 = zCoord(momentumA, positionA, ra, xca, yca, xg2, yg2);
    double zb2 = zCoord(momentumB, positionB, rb, xcb, ycb, xg2, yg2);

    if (abs(zb1 - za1) < abs(zb2 - za2)) {
      xga = xg1; yga = yg1; zga = za1; zgb = zb1;
    }
    else {
      xga = xg2; yga = yg2; zga = za2; zgb = zb2;
    }
    xgb = xga; ygb = yga;
  }
  else {
    // one point of closest approach on each track in transverse plane
    xga = xg1; yga = yg1;
    zga = zCoord(momentumA, positionA, ra, xca, yca, xga, yga);
    xgb = xg2; ygb = yg2;
    zgb = zCoord(momentumB, positionB, rb, xcb, ycb, xgb, ygb);
  }

  posA = GlobalPoint(xga, yga, zga);
  posB = GlobalPoint(xgb, ygb, zgb);
  status_ = true;
  return true;
}

GlobalPoint ClosestApproachInRPhi::crossingPoint ( ) const

virtual

arithmetic mean of the two points of closest approach

Implements ClosestApproachOnHelices.

Definition at line 52 of file ClosestApproachInRPhi.cc.

References edm::hlt::Exception.

Referenced by NuclearVertexBuilder::FillVertexWithCrossingPoint(), V0Fitter::fitAll(), NuclearVertexBuilder::isGoodSecondaryTrack(), and ConversionProducer::preselectTrackPair().

{
  if (!status_)
    throw cms::Exception("TrackingTools/PatternTools","ClosestApproachInRPhi::could not compute track crossing. Check status before calling this method!");
  return  GlobalPoint(0.5*(posA.basicVector() + posB.basicVector()));
             
}

float ClosestApproachInRPhi::distance ( ) const

virtual

distance between the two points of closest approach in 3D

Implements ClosestApproachOnHelices.

Definition at line 61 of file ClosestApproachInRPhi.cc.

References edm::hlt::Exception.

Referenced by HLTMuon::analyze(), V0Fitter::fitAll(), HLTMuonTrackMassFilter::hltFilter(), HLTMuonDimuonL3Filter::hltFilter(), HLTMuonTrimuonL3Filter::hltFilter(), NuclearVertexBuilder::isGoodSecondaryTrack(), and print().

{
  if (!status_)
    throw cms::Exception("TrackingTools/PatternTools","ClosestApproachInRPhi::could not compute track crossing. Check status before calling this method!");
  return (posB - posA).mag();
}

GlobalTrajectoryParameters ClosestApproachInRPhi::newTrajectory ( const GlobalPoint &  newpt, const GlobalTrajectoryParameters &  oldpar, double  bz  )

staticprivate

Definition at line 136 of file ClosestApproachInRPhi.cc.

References GlobalTrajectoryParameters::charge(), GlobalTrajectoryParameters::magneticField(), GlobalTrajectoryParameters::momentum(), GlobalTrajectoryParameters::position(), PV3DBase< T, PVType, FrameType >::x(), PV3DBase< T, PVType, FrameType >::y(), and PV3DBase< T, PVType, FrameType >::z().

{
  // First we need the centers of the circles.
  double qob = oldgtp.charge()/bz;
  double xc =  oldgtp.position().x() + qob *  oldgtp.momentum().y();
  double yc =  oldgtp.position().y() - qob *  oldgtp.momentum().x();

  // and of course....  
  double npx = (newpt.y()-yc)*(bz/oldgtp.charge());
  double npy = (xc-newpt.x())*(bz/oldgtp.charge());
 
  /*
   * old code: slow and wrong
   *
  // now we do a translation, move the center of circle to (0,0,0).
  double dx1 = oldgtp.position().x() - xc;
  double dy1 = oldgtp.position().y() - yc;
  double dx2 = newpt.x() - xc;
  double dy2 = newpt.y() - yc;
 
  // now for the angles:
  double cosphi = ( dx1 * dx2 + dy1 * dy2 ) / 
    ( sqrt ( dx1 * dx1 + dy1 * dy1 ) * sqrt ( dx2 * dx2 + dy2 * dy2 ));
  double sinphi = - oldgtp.charge() * sqrt ( 1 - cosphi * cosphi );
  
  // Finally, the new momenta:
  double px = cosphi * oldgtp.momentum().x() - sinphi * oldgtp.momentum().y();
  double py = sinphi * oldgtp.momentum().x() + cosphi * oldgtp.momentum().y();
  
  std::cout << px-npx << " " << py-npy << ", " << oldgtp.charge() << std::endl;
  */

  GlobalVector vta ( npx, npy, oldgtp.momentum().z() );
  GlobalTrajectoryParameters gta( newpt , vta , oldgtp.charge(), &(oldgtp.magneticField()) );
  return gta;
}

pair< GlobalPoint, GlobalPoint > ClosestApproachInRPhi::points ( ) const

virtual

Returns the two PCA on the trajectories.

Implements ClosestApproachOnHelices.

Definition at line 43 of file ClosestApproachInRPhi.cc.

References edm::hlt::Exception.

{
  if (!status_)
    throw cms::Exception("TrackingTools/PatternTools","ClosestApproachInRPhi::could not compute track crossing. Check status before calling this method!");
  return  pair<GlobalPoint, GlobalPoint> (posA, posB);
}

virtual bool ClosestApproachInRPhi::status ( void  ) const

inlinevirtual

Implements ClosestApproachOnHelices.

Definition at line 30 of file ClosestApproachInRPhi.h.

References status_.

Referenced by HLTMuon::analyze(), V0Fitter::fitAll(), HLTMuonTrackMassFilter::hltFilter(), HLTMuonTrimuonL3Filter::hltFilter(), HLTMuonDimuonL3Filter::hltFilter(), and ConversionProducer::preselectTrackPair().

{return status_;}

pair< GlobalTrajectoryParameters, GlobalTrajectoryParameters > ClosestApproachInRPhi::trajectoryParameters

(

)

const

Returns not only the points, but the full GlobalTrajectoryParemeters at the points of closest approach

Definition at line 125 of file ClosestApproachInRPhi.cc.

References edm::hlt::Exception, and run_regression::ret.

{
  if (!status_)
    throw cms::Exception("TrackingTools/PatternTools","ClosestApproachInRPhi::could not compute track crossing. Check status before calling this method!");
  pair <GlobalTrajectoryParameters, GlobalTrajectoryParameters> 
    ret ( newTrajectory( posA, paramA, bz),
          newTrajectory( posB, paramB, bz) );
  return ret;
}

int ClosestApproachInRPhi::transverseCoord ( double  cxa, double  cya, double  ra, double  cxb, double  cyb, double  rb, double &  xg1, double &  yg1, double &  xg2, double &  yg2  )

staticprivate

Definition at line 205 of file ClosestApproachInRPhi.cc.

References abs, mathSSE::sqrt(), and v.

{
  int flag = 0;
  double x1, y1, x2, y2;

  // new reference frame with origin in (cxa, cya) and x-axis 
  // directed from (cxa, cya) to (cxb, cyb)

  double d_ab = sqrt((cxb - cxa)*(cxb - cxa) + (cyb - cya)*(cyb - cya));
  if (d_ab == 0) { // concentric circles
    return 0;
  }
  // elements of rotation matrix
  double u = (cxb - cxa) / d_ab;
  double v = (cyb - cya) / d_ab;

  // conditions for circle intersection
  if (d_ab <= ra + rb && d_ab >= abs(rb - ra)) {

    // circles cross each other
    flag = 1;

    // triangle (ra, rb, d_ab)
    double cosphi = (ra*ra - rb*rb + d_ab*d_ab) / (2*ra*d_ab);
    double sinphi2 = 1. - cosphi*cosphi;
    if (sinphi2 < 0.) { sinphi2 = 0.; cosphi = 1.; }

    // intersection points in new frame
    double sinphi = sqrt(sinphi2);
    x1 = ra*cosphi; y1 = ra*sinphi; x2 = x1; y2 = -y1;
  } 
  else if (d_ab > ra + rb) {

    // circles are external to each other
    flag = 2;

    // points of closest approach in new frame 
    // are on line between 2 centers
    x1 = ra; y1 = 0; x2 = d_ab - rb; y2 = 0;
  }
  else if (d_ab < abs(rb - ra)) {

    // circles are inside each other
    flag = 2;

    // points of closest approach in new frame are on line between 2 centers
    // choose 2 closest points
    double sign = 1.;
    if (ra <= rb) sign = -1.;
    x1 = sign*ra; y1 = 0; x2 = d_ab + sign*rb; y2 = 0;
  }
  else {
    return 0;
  }

  // intersection points in global frame, transverse plane
  xg1 = u*x1 - v*y1 + cxa; yg1 = v*x1 + u*y1 + cya;
  xg2 = u*x2 - v*y2 + cxa; yg2 = v*x2 + u*y2 + cya;

  return flag;
}

double ClosestApproachInRPhi::zCoord ( const GlobalVector &  mom, const GlobalPoint &  pos, double  r, double  xc, double  yc, double  xg, double  yg  )

staticprivate

Definition at line 272 of file ClosestApproachInRPhi.cc.

References abs, phi, alignCSCRings::r, mathSSE::sqrt(), PV3DBase< T, PVType, FrameType >::transverse(), x, PV3DBase< T, PVType, FrameType >::x(), detailsBasic3DVector::y, PV3DBase< T, PVType, FrameType >::y(), detailsBasic3DVector::z, and PV3DBase< T, PVType, FrameType >::z().

{

  // starting point
  double x = pos.x(); double y = pos.y(); double z = pos.z();

  double px = mom.x(); double py = mom.y(); double pz = mom.z();

  // rotation angle phi from starting point to crossing point (absolute value)
  // -- compute sin(phi/2) if phi smaller than pi/4, 
  // -- cos(phi) if phi larger than pi/4
  double phi = 0.;
  double sinHalfPhi = sqrt((x-xg)*(x-xg) + (y-yg)*(y-yg))/(2*r);
  if (sinHalfPhi < 0.383) { // sin(pi/8)
    phi = 2*asin(sinHalfPhi);
  }
  else {
    double cosPhi = ((x-xc)*(xg-xc) + (y-yc)*(yg-yc))/(r*r);
    if (std::abs(cosPhi) > 1) cosPhi = (cosPhi > 0 ? 1 : -1);
    phi = abs(acos(cosPhi));
  }
  // -- sign of phi
  double signPhi = ((x - xc)*(yg - yc) - (xg - xc)*(y - yc) > 0) ? 1. : -1.;

  // sign of track angular momentum
  // if rotation is along angular momentum, delta z is along pz
  double signOmega = ((x - xc)*py - (y - yc)*px > 0) ? 1. : -1.;

  // delta z
  // -- |dz| = |cos(theta) * path along helix|
  //         = |cos(theta) * arc length along circle / sin(theta)|
  double dz = signPhi*signOmega*(pz/mom.transverse())*phi*r;

  return z + dz;
}

Member Data Documentation

double ClosestApproachInRPhi::bz

private

Definition at line 99 of file ClosestApproachInRPhi.h.

GlobalTrajectoryParameters ClosestApproachInRPhi::paramA

private

Definition at line 98 of file ClosestApproachInRPhi.h.

GlobalTrajectoryParameters ClosestApproachInRPhi::paramB

private

Definition at line 98 of file ClosestApproachInRPhi.h.

GlobalPoint ClosestApproachInRPhi::posA

private

Definition at line 97 of file ClosestApproachInRPhi.h.

GlobalPoint ClosestApproachInRPhi::posB

private

Definition at line 97 of file ClosestApproachInRPhi.h.

bool ClosestApproachInRPhi::status_

private

Definition at line 100 of file ClosestApproachInRPhi.h.

Referenced by ClosestApproachInRPhi(), and status().