Utility for propagation of a particle along helix. More...

#include <HelixSwimmer.h>

Collaboration diagram for HelixSwimmer:

Public Member Functions
	HelixSwimmer ()
	default constructor

void	set (const TVector3 &position, const TVector3 &momentum, double charge, double Bz)
	Sets the helix. More...

void	setTransformation (const TRotation &rotation, const TVector3 &translation)
	Sets transformation from the frame in which helix is constructed to module local frame. More...

void	moveReferencePosition (double length)
	Moves reference position along helix by length. More...

TVector3	getPosition (double length) const
	Returns particle position at given length. More...

TVector3	getDirection (double length) const
	Returns particle direction at given length. More...

double	getDistanceToPlane (const TVector3 &point, const TVector3 &normal) const
	Returns the distance along helix to the nearest intersection with a plane nearly parallel to z axis. More...

Private Member Functions
double	shortestDistance (double cosAlpha, double phi) const
	Returns shortest distance. More...

double	withinSingleTurn (double t) const
	Returns helix length within a single turn. More...

Private Attributes
double	m_R = 0
	helix radius

double	m_xc = 0
	helix axis position in x

double	m_yc = 0
	helix axis position in y

double	m_omega = 0
	angular speed [1/cm]

double	m_kz = 0
	slope in z

double	m_phi0 = 0
	phi of reference position

double	m_z0 = 0
	z of reference position

double	m_T0 = 0
	helix length of single turn

double &	x0 = m_xc
	x of reference position for zero magnetic field

double &	y0 = m_yc
	y of reference position for zero magnetic field

double &	z0 = m_z0
	z of reference position for zero magnetic field

double &	kx = m_R
	direction in x for zero magnetic field

double &	ky = m_phi0
	direction in y for zero magnetic field

double &	kz = m_kz
	direction in z for zero magnetic field

TRotation	m_rotationInv
	inverse of rotation matrix

TVector3	m_translation
	translation vector

Detailed Description

Utility for propagation of a particle along helix.

Helix representation here differs from the official one. Running parameter is the signed distance along helix measured from the reference position. Negative distance means propagating back in time.

Definition at line 29 of file HelixSwimmer.h.

Member Function Documentation

◆ getDirection()

TVector3 getDirection ( double length ) const

Returns particle direction at given length.

Parameters

length distance along helix measured from the reference position

Returns: direction (in module local frame if transformation is set)

Definition at line 79 of file HelixSwimmer.cc.

     {
       if (m_omega != 0) {
         double phi = m_phi0 + m_omega * length;
         double k_T = m_omega * m_R;
         TVector3 vec(-k_T * sin(phi), k_T * cos(phi), m_kz);
         return m_rotationInv * vec;
       } else {
         TVector3 vec(kx, ky, kz);
         return m_rotationInv * vec;
       }
     }

◆ getDistanceToPlane()

double getDistanceToPlane	(	const TVector3 &	point,
		const TVector3 &	normal
	)		const

Returns the distance along helix to the nearest intersection with a plane nearly parallel to z axis.

Parameters

point	point on the plane
normal	plane normal

Returns: signed distance (NaN if cross-section doesn't exist)

Definition at line 92 of file HelixSwimmer.cc.

◆ getPosition()

TVector3 getPosition ( double length ) const

Returns particle position at given length.

Parameters

length distance along helix measured from the reference position

Returns: position (in module local frame if transformation is set)

Definition at line 67 of file HelixSwimmer.cc.

◆ moveReferencePosition()

void moveReferencePosition ( double length )

Moves reference position along helix by length.

Parameters

length distance along helix measured from current reference position

Definition at line 55 of file HelixSwimmer.cc.

◆ set()

void set	(	const TVector3 &	position,
		const TVector3 &	momentum,
		double	charge,
		double	Bz
	)

Sets the helix.

Parameters

position	particle position (= default reference position)
momentum	particle momentum
charge	particle charge in units of elementary charge
Bz	magnetic field z-component (we assume other two are negligible)

Definition at line 24 of file HelixSwimmer.cc.

◆ setTransformation()

void setTransformation	(	const TRotation &	rotation,
		const TVector3 &	translation
	)

Sets transformation from the frame in which helix is constructed to module local frame.

Transformation is: inverse translation first then inverse rotation

Parameters

rotation	rotation matrix
translation	translation vector

Definition at line 49 of file HelixSwimmer.cc.

◆ shortestDistance()

double shortestDistance	(	double	cosAlpha,
		double	phi
	)		const

inlineprivate

Returns shortest distance.

Parameters

cosAlpha	cosine of alpha
phi	phi of plane

Returns: signed shortest distance

Definition at line 123 of file HelixSwimmer.h.

     {
       double alpha = acos(cosAlpha);
       double t1 = withinSingleTurn((phi - m_phi0 - alpha) / m_omega);
       double t2 = withinSingleTurn((phi - m_phi0 + alpha) / m_omega);
       double ta = std::min(t1, t2);
       double tb = std::max(t1 - m_T0, t2 - m_T0);
       double t = (abs(ta) < abs(tb)) ? ta : tb;
       return t;
     }

◆ withinSingleTurn()

double withinSingleTurn ( double t ) const

inlineprivate

Returns helix length within a single turn.

Parameters

t	helix length

Returns: helix length within single turn

Definition at line 134 of file HelixSwimmer.h.

The documentation for this class was generated from the following files:

top/reconstruction_cpp/include/HelixSwimmer.h
top/reconstruction_cpp/src/HelixSwimmer.cc

Public Member Functions

Private Member Functions

Private Attributes

Detailed Description

Member Function Documentation

◆ getDirection()

◆ getDistanceToPlane()

◆ getPosition()

◆ moveReferencePosition()

◆ set()

◆ setTransformation()

◆ shortestDistance()

◆ withinSingleTurn()