Estimator for impact point calculations A description of the underlying mathematics can be found here: https://github.com/acts-project/acts/pull/2506 TODO: Upload reference at a better place. More...

#include <Acts/Vertexing/ImpactPointEstimator.hpp>

Classes
struct	Config
struct	State
	State struct. More...

Public Member Functions
	ImpactPointEstimator (const Config &cfg, std::unique_ptr< const Logger > logger=getDefaultLogger("ImpactPointEstimator", Logging::INFO))
	Constructor.
	ImpactPointEstimator (const ImpactPointEstimator &other)
	Copy constructor to clone logger (class owns a unique pointer to it, which can't be copied).
	ImpactPointEstimator (ImpactPointEstimator &&)=default
	Move constructor for impact point estimator.
Result< double >	calculateDistance (const GeometryContext &gctx, const BoundTrackParameters &trkParams, const Vector3 &vtxPos, State &state) const
	Calculates 3D distance between a track and a vertex.
Result< BoundTrackParameters >	estimate3DImpactParameters (const GeometryContext &gctx, const Acts::MagneticFieldContext &mctx, const BoundTrackParameters &trkParams, const Vector3 &vtxPos, State &state) const
	Estimates the track parameters at the 3D PCA (i.e., a point of minimal 3D distance) to a vertex.
Result< double >	get3DLifetimeSignOfTrack (const BoundTrackParameters &track, const Vertex &vtx, const Acts::Vector3 &direction, const GeometryContext &gctx, const MagneticFieldContext &mctx) const
	Estimates the sign of the 3D lifetime of a given track w.r.t.
template<int nDim>
Result< std::pair< Acts::ActsVector< nDim >, Acts::Vector3 > >	getDistanceAndMomentum (const GeometryContext &gctx, const BoundTrackParameters &trkParams, const ActsVector< nDim > &vtxPos, State &state) const
	Calculate the distance between a track and a vertex by finding the corresponding 3D PCA.
Result< ImpactParametersAndSigma >	getImpactParameters (const BoundTrackParameters &track, const Vertex &vtx, const GeometryContext &gctx, const MagneticFieldContext &mctx, bool calculateTimeIP=false) const
	Calculates the impact parameters of a track w.r.t.
Result< std::pair< double, double > >	getLifetimeSignOfTrack (const BoundTrackParameters &track, const Vertex &vtx, const Acts::Vector3 &direction, const GeometryContext &gctx, const MagneticFieldContext &mctx) const
	Estimates the sign of the 2D and Z lifetime of a given track w.r.t.
template<int nDim>
Result< double >	getVertexCompatibility (const GeometryContext &gctx, const BoundTrackParameters *trkParams, const ActsVector< nDim > &vertexPos) const
	Estimates the compatibility of a track to a vertex based on their 3D (if nDim = 3) or 4D (if nDim = 4) distance and the track covariance.

Detailed Description

Estimator for impact point calculations A description of the underlying mathematics can be found here: https://github.com/acts-project/acts/pull/2506 TODO: Upload reference at a better place.

Constructor & Destructor Documentation

◆ ImpactPointEstimator() [1/3]

Acts::ImpactPointEstimator::ImpactPointEstimator	(	const Config &	cfg,
		std::unique_ptr< const Logger >	logger = getDefaultLogger("ImpactPointEstimator", Logging::INFO) )

explicit

Constructor.

Parameters

cfg	Configuration object
logger	Logging instance

◆ ImpactPointEstimator() [2/3]

Acts::ImpactPointEstimator::ImpactPointEstimator ( const ImpactPointEstimator & other )

Copy constructor to clone logger (class owns a unique pointer to it, which can't be copied).

Parameters

other Impact point estimator to be cloned

◆ ImpactPointEstimator() [3/3]

Acts::ImpactPointEstimator::ImpactPointEstimator ( ImpactPointEstimator && )

default

Move constructor for impact point estimator.

Member Function Documentation

◆ calculateDistance()

Result< double > Acts::ImpactPointEstimator::calculateDistance	(	const GeometryContext &	gctx,
		const BoundTrackParameters &	trkParams,
		const Vector3 &	vtxPos,
		State &	state ) const

Calculates 3D distance between a track and a vertex.

Parameters

gctx	The geometry context
trkParams	Track parameters
vtxPos	3D position to calculate the distance to
state	The state object

Returns: Distance

◆ estimate3DImpactParameters()

Result< BoundTrackParameters > Acts::ImpactPointEstimator::estimate3DImpactParameters	(	const GeometryContext &	gctx,
		const Acts::MagneticFieldContext &	mctx,
		const BoundTrackParameters &	trkParams,
		const Vector3 &	vtxPos,
		State &	state ) const

Estimates the track parameters at the 3D PCA (i.e., a point of minimal 3D distance) to a vertex.

The track parameters are defined wrt a reference plane that has its origin at the vertex position and whose z-axis points in the direction of the track momentum. The plane's x-axis points approximately from the vertex to the 3D PCA (it is only approximate because we force it to be orthogonal to the z-axis). The y-axis is calculated as a cross product between x- and z-axis.

Parameters

gctx	The geometry context
mctx	The magnetic field context
trkParams	Track parameters
vtxPos	Reference position (vertex)
state	The state object

Returns: Track parameters at the 3D PCA

◆ get3DLifetimeSignOfTrack()

Result< double > Acts::ImpactPointEstimator::get3DLifetimeSignOfTrack	(	const BoundTrackParameters &	track,
		const Vertex &	vtx,
		const Acts::Vector3 &	direction,
		const GeometryContext &	gctx,
		const MagneticFieldContext &	mctx ) const

Estimates the sign of the 3D lifetime of a given track w.r.t.

a vertex and a direction (e.g. a jet direction)

Parameters

track	Track to estimate the IP from
vtx	Vertex the track belongs to
direction	The direction
gctx	The geometry context
mctx	The magnetic field context

Returns: The value of the 3D lifetime

◆ getDistanceAndMomentum()

template<int nDim>

Result< std::pair< Acts::ActsVector< nDim >, Acts::Vector3 > > Acts::ImpactPointEstimator::getDistanceAndMomentum	(	const GeometryContext &	gctx,
		const BoundTrackParameters &	trkParams,
		const ActsVector< nDim > &	vtxPos,
		State &	state ) const

Calculate the distance between a track and a vertex by finding the corresponding 3D PCA.

Returns also the momentum direction at the 3D PCA. The template parameter nDim determines whether we calculate the 3D distance (nDim = 3) or the 4D distance (nDim = 4) to the 3D PCA.

Note: For straight tracks we use an analytical solution; for helical tracks we use the Newton method.

Template Parameters

nDim	Number of dimensions used to compute compatibility

Note: If nDim = 3 we only consider spatial dimensions; if nDim = 4, we also consider time. Other values are not allowed.

Parameters

gctx	Geometry context
trkParams	Track parameters
vtxPos	Vertex position
state	The state object

Returns: Pair containing the distance vector and momentum direction at PCA

◆ getImpactParameters()

Result< ImpactParametersAndSigma > Acts::ImpactPointEstimator::getImpactParameters	(	const BoundTrackParameters &	track,
		const Vertex &	vtx,
		const GeometryContext &	gctx,
		const MagneticFieldContext &	mctx,
		bool	calculateTimeIP = false ) const

Calculates the impact parameters of a track w.r.t.

a vertex. The corresponding errors are approximated by summing the variances of the track and the vertex.

Parameters

track	Track whose impact parameters are calculated
vtx	Vertex corresponding to the track
gctx	The geometry context
mctx	The magnetic field context
calculateTimeIP	If true, the difference in time is computed

Returns: Impact parameters and their uncertainties for the track-vertex pair

◆ getLifetimeSignOfTrack()

Result< std::pair< double, double > > Acts::ImpactPointEstimator::getLifetimeSignOfTrack	(	const BoundTrackParameters &	track,
		const Vertex &	vtx,
		const Acts::Vector3 &	direction,
		const GeometryContext &	gctx,
		const MagneticFieldContext &	mctx ) const

Estimates the sign of the 2D and Z lifetime of a given track w.r.t.

a vertex and a direction (e.g. a jet direction) by propagating the trajectory state towards the vertex position and computing the scalar product with the direction vector

Parameters

track	Track to estimate the IP from
vtx	Vertex the track belongs to
direction	The direction
gctx	The geometry context
mctx	The magnetic field context

Returns: A pair holding the sign for the 2D and Z lifetimes

◆ getVertexCompatibility()

template<int nDim>

Result< double > Acts::ImpactPointEstimator::getVertexCompatibility	(	const GeometryContext &	gctx,
		const BoundTrackParameters *	trkParams,
		const ActsVector< nDim > &	vertexPos ) const

Estimates the compatibility of a track to a vertex based on their 3D (if nDim = 3) or 4D (if nDim = 4) distance and the track covariance.

Note: Confusingly, a smaller compatibility means that a track is more compatible.

Template Parameters

nDim	Number of dimensions used to compute compatibility

Note: If nDim = 3 we only consider spatial dimensions; if nDim = 4, we also consider time. Other values are not allowed.

Parameters

gctx	The Geometry context
trkParams	Track parameters at point of closest approach in 3D as retrieved by estimate3DImpactParameters
vertexPos	The vertex position

Returns: The compatibility value

Classes

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

◆ ImpactPointEstimator() [1/3]

◆ ImpactPointEstimator() [2/3]

◆ ImpactPointEstimator() [3/3]

Member Function Documentation

◆ calculateDistance()

◆ estimate3DImpactParameters()

◆ get3DLifetimeSignOfTrack()

◆ getDistanceAndMomentum()

◆ getImpactParameters()

◆ getLifetimeSignOfTrack()

◆ getVertexCompatibility()