fastsim::Trajectory Class Reference

Definition the generic trajectory of a particle (base class for helix/straight trajectories). More...

#include <Trajectory.h>

Inheritance diagram for fastsim::Trajectory:

Public Member Functions
virtual bool	crosses (const BarrelSimplifiedGeometry &layer) const =0
	Check if trajectory crosses a barrel layer. More...
const math::XYZTLorentzVector &	getMomentum ()
	Simple getter: return momentum of the particle that was used to create trajectory. More...
const math::XYZTLorentzVector &	getPosition ()
	Simple getter: return position of the particle that was used to create trajectory. More...
virtual void	move (double deltaTimeC)=0
	Move the particle along the trajectory for a given time. More...
virtual double	nextCrossingTimeC (const BarrelSimplifiedGeometry &layer, bool onLayer=false) const =0
	Return delta time (t*c) of the next intersection of trajectory and barrel layer. More...
double	nextCrossingTimeC (const ForwardSimplifiedGeometry &layer, bool onLayer=false) const
	Return delta time (t*c) of the next intersection of trajectory and forward layer. More...
double	nextCrossingTimeC (const SimplifiedGeometry &layer, bool onLayer=false) const
	Return delta time (t*c) of the next intersection of trajectory and generic layer. More...
virtual	~Trajectory ()

Static Public Member Functions
static std::unique_ptr< Trajectory >	createTrajectory (const fastsim::Particle &particle, const double magneticFieldZ)
	Calls constructor of derived classes. More...

Protected Member Functions
	Trajectory (const fastsim::Particle &particle)
	Constructor of base class. More...

Protected Attributes
math::XYZTLorentzVector	momentum_
	momentum of the particle that was used to create trajectory More...
math::XYZTLorentzVector	position_
	position of the particle that was used to create trajectory More...

Detailed Description

Definition the generic trajectory of a particle (base class for helix/straight trajectories).

Mathematical representation of a particle's trajectory. Provides three basic funtions:

• Check if an intersection between a trajectory and a layer exists
• Get the time when this happens (delta time in units of t*c)
• Move the particle along it's trajectory for a given time (delta time in units of t*c)

Definition at line 26 of file Trajectory.h.

Constructor & Destructor Documentation

~Trajectory()

Trajectory::~Trajectory ( )

virtual

Definition at line 10 of file Trajectory.cc.

{}

Trajectory()

Trajectory::Trajectory ( const fastsim::Particle &  particle )

protected

Constructor of base class.

Usually constructor of derived classes HelixTrajectory or StraightTrajectory are called.

Definition at line 12 of file Trajectory.cc.

                                                             {
  position_ = particle.position();
  momentum_ = particle.momentum();
}

References fastsim::Particle::momentum(), and fastsim::Particle::position().

Member Function Documentation

createTrajectory()

std::unique_ptr< fastsim::Trajectory > Trajectory::createTrajectory ( const fastsim::Particle &  particle, const double  magneticFieldZ  )

static

Calls constructor of derived classes.

Decides whether a straight (uncharged particle or very high pT charged particle) or a helix trajectory (generic charged particle) is constructed.

Parameters

particle	The particle that should be decayed.
magneticFieldZ	The strenght of the magnetic field at the position of the particle.

Returns

A StraightTrajectory or a HelixTrajectory

Definition at line 17 of file Trajectory.cc.

                                                                                                  {
  if (particle.charge() == 0. || magneticFieldZ == 0.) {
    LogDebug("FastSim") << "create straight trajectory";
    return std::unique_ptr<fastsim::Trajectory>(new fastsim::StraightTrajectory(particle));
  } else if (std::abs(particle.momentum().Pt() /
                      (fastsim::Constants::speedOfLight * 1e-4 * particle.charge() * magneticFieldZ)) > 1e5) {
    LogDebug("FastSim") << "create straight trajectory (huge radius)";
    return std::unique_ptr<fastsim::Trajectory>(new fastsim::StraightTrajectory(particle));
  } else {
    LogDebug("FastSim") << "create helix trajectory";
    return std::unique_ptr<fastsim::Trajectory>(new fastsim::HelixTrajectory(particle, magneticFieldZ));
  }
}

References funct::abs(), fastsim::Particle::charge(), MillePedeFileConverter_cfg::e, LogDebug, CaloMaterial_cfi::magneticFieldZ, fastsim::Particle::momentum(), and fastsim::Constants::speedOfLight.

Referenced by fastsim::LayerNavigator::moveParticleToNextLayer().

crosses()

virtual bool fastsim::Trajectory::crosses ( const BarrelSimplifiedGeometry &  layer ) const

pure virtual

Check if trajectory crosses a barrel layer.

Virtual function since different behavior of straight and helix trajectory. This funtion does not exist for forward layers since those are always hit - unless particle has exactly 0 momentum in Z direction which doesn't happen for numerical reasons.

Implemented in fastsim::StraightTrajectory, and fastsim::HelixTrajectory.

getMomentum()

const math::XYZTLorentzVector& fastsim::Trajectory::getMomentum ( )

inline

Simple getter: return momentum of the particle that was used to create trajectory.

Definition at line 48 of file Trajectory.h.

{ return momentum_; }

References momentum_.

getPosition()

const math::XYZTLorentzVector& fastsim::Trajectory::getPosition ( )

inline

Simple getter: return position of the particle that was used to create trajectory.

Definition at line 45 of file Trajectory.h.

{ return position_; }

References position_.

move()

virtual void fastsim::Trajectory::move ( double  deltaTimeC )

pure virtual

Move the particle along the trajectory for a given time.

Parameters

deltaTimeC

Time in units of t*c..

Implemented in fastsim::StraightTrajectory, and fastsim::HelixTrajectory.

nextCrossingTimeC() [1/3]

virtual double fastsim::Trajectory::nextCrossingTimeC ( const BarrelSimplifiedGeometry &  layer, bool  onLayer = false  ) const

pure virtual

Return delta time (t*c) of the next intersection of trajectory and barrel layer.

Different treatment of intersection of straight/helix layers with barrel layers. Implementation in derived classes.

Parameters

layer	A barrel layer.
onLayer	Specify if the particle already is on the layer (in that case the second solution has to be picked).

Returns

t*c [ns * cm/ns] of next intersection (-1 if there is none).

Implemented in fastsim::StraightTrajectory, and fastsim::HelixTrajectory.

nextCrossingTimeC() [2/3]

double Trajectory::nextCrossingTimeC	(	const ForwardSimplifiedGeometry &	layer,
		bool	onLayer = false
	)		const

Return delta time (t*c) of the next intersection of trajectory and forward layer.

Since only momentum in Z direction matters, same function for straight and helix trajectories.

Parameters

layer	A forward layer.
onLayer	Specify if the particle already is on the layer (in this case there is no solution).

Returns

t*c [ns * cm/ns] of next intersection (-1 if there is none).

Definition at line 40 of file Trajectory.cc.

                                                                                                             {
  if (onLayer) {
    return -1;
  }
  // t = (z - z_0) / v_z
  // substitute: v_z = p_z / E * c  ( note: extra * c absorbed in p_z units)
  // => t*c = (z - z_0) / p_z * E
  double deltaTimeC = (layer.getZ() - position_.Z()) / momentum_.Z() * momentum_.E();
  return deltaTimeC > 0. ? deltaTimeC : -1.;
}

References fastsim::ForwardSimplifiedGeometry::getZ().

nextCrossingTimeC() [3/3]

double Trajectory::nextCrossingTimeC	(	const SimplifiedGeometry &	layer,
		bool	onLayer = false
	)		const

Return delta time (t*c) of the next intersection of trajectory and generic layer.

Calculation different for barrel/forward layers and straight/helix trajectory. Chooses which function has to be called.

Parameters

layer	A barrel or forward layer.
onLayer	Specify if the particle already is on the layer (leads to different constraints for forward/barrel layers).

Returns

t*c [ns * cm/ns] of next intersection (-1 if there is none).

Definition at line 32 of file Trajectory.cc.

                                                                                                      {
  if (layer.isForward()) {
    return this->nextCrossingTimeC(static_cast<const fastsim::ForwardSimplifiedGeometry &>(layer), onLayer);
  } else {
    return this->nextCrossingTimeC(static_cast<const fastsim::BarrelSimplifiedGeometry &>(layer), onLayer);
  }
}

References fastsim::SimplifiedGeometry::isForward().

Member Data Documentation

momentum_

math::XYZTLorentzVector fastsim::Trajectory::momentum_

protected

momentum of the particle that was used to create trajectory

Definition at line 92 of file Trajectory.h.

Referenced by getMomentum(), and fastsim::StraightTrajectory::nextCrossingTimeC().

position_

math::XYZTLorentzVector fastsim::Trajectory::position_

protected

position of the particle that was used to create trajectory

Definition at line 91 of file Trajectory.h.

Referenced by getPosition(), and fastsim::StraightTrajectory::nextCrossingTimeC().