trkf::InteractPlane Class Reference

#include "InteractPlane.h"

Inheritance diagram for trkf::InteractPlane:

Public Member Functions
	InteractPlane (double tcut)
	Constructor. More...
virtual	~InteractPlane ()
	Destructor. More...
Interactor *	clone () const
	Clone method. More...
virtual bool	noise (const KTrack &trk, double s, TrackError &noise_matrix) const
	Calculate noise matrix. More...
double	getTcut () const

Detailed Description

Definition at line 23 of file InteractPlane.h.

Constructor & Destructor Documentation

trkf::InteractPlane::InteractPlane

(

double

tcut

)

Constructor.

Constructor.

Arguments:

tcut - Maximum delta ray energy.

Definition at line 26 of file InteractPlane.cxx.

Referenced by clone().

                                          :
    Interactor(tcut)
  {}

trkf::InteractPlane::~InteractPlane ( )

virtual

Destructor.

Definition at line 31 of file InteractPlane.cxx.

  {}

Member Function Documentation

Interactor* trkf::InteractPlane::clone ( ) const

inlinevirtual

Clone method.

Implements trkf::Interactor.

Definition at line 36 of file InteractPlane.h.

References InteractPlane(), noise(), and s.

{return new InteractPlane(*this);}

double trkf::Interactor::getTcut ( ) const

inlineinherited

Definition at line 39 of file Interactor.h.

References trkf::Interactor::clone(), trkf::Interactor::fTcut, trkf::Interactor::noise(), and s.

Referenced by noise().

{return fTcut;}

bool trkf::InteractPlane::noise ( const KTrack &  trk, double  s, TrackError &  noise_matrix  ) const

virtual

Calculate noise matrix.

Calculate noise matrix.

Arguments:

trk - Original track. s - Path distance. noise_matrix - Resultant noise matrix.

Returns: True if success.

Currently calculate noise from multiple scattering only.

Note about multiple scattering calculation:

In the case of normal incident track (u' = v' = 0), the multiple scattering calculations used in this class reduce to the familiar small-angle formulas found in the particle data book for a thick scatterer (meaning multiple scattering modifies both position and slope errors). However, the distance used in the logarithm factor of the rms scattering angle is an estimate of the total track length, rather than the incremental track length.

For non-normal incident track, the error ellipse is elongated in the radial direciton of the uv plane by factor sqrt(1 + u'^2 + v'^2). This is equivalent to expansion in the u direction by factor sqrt(1 + u'^2), and expansion in the v direction by sqrt(1 + v'^2), with uv correlation u' v' / sqrt((1 + u'^2)(1 + v'^2)).

Correlation between position and slope in the same view is sqrt(3)/2 regardless of normal incidence.

Correlation between position and slope in the opposite view is (sqrt(3)/2) u' v' / sqrt((1 + u'^2)(1 + v'^2))

Implements trkf::Interactor.

Definition at line 70 of file InteractPlane.cxx.

References trkf::Surface::BACKWARD, e, trkf::KTrack::getDirection(), trkf::KTrack::getSurface(), trkf::Interactor::getTcut(), trkf::KTrack::getVector(), and trkf::KTrack::Mass().

Referenced by clone(), and trkf::InteractGeneral::noise().

  {
    // Get LAr service.

    auto const * larprop = lar::providerFrom<detinfo::LArPropertiesService>();
    auto const * detprop = lar::providerFrom<detinfo::DetectorPropertiesService>();

    // Make sure we are on a plane surface (throw exception if not).

    const SurfPlane* psurf = dynamic_cast<const SurfPlane*>(&*trk.getSurface());
    if(psurf == 0)
      throw cet::exception("InteractPlane") 
        << "InteractPlane called for non-planar surface.\n";

    // Clear noise matrix.

    noise_matrix.clear();

    // Unpack track parameters.

    const TrackVector& vec = trk.getVector();
    double dudw = vec[2];
    double dvdw = vec[3];
    double pinv = vec[4];
    double mass = trk.Mass();

    // If distance is zero, or momentum is infinite, return zero noise.

    if(pinv == 0. || s == 0.)
      return true;

    // Make a crude estimate of the range of the track.

    double p = 1./std::abs(pinv);
    double p2 = p*p;
    double e2 = p2 + mass*mass;
    double e = std::sqrt(e2);
    double t = e - mass;
    double dedx = 0.001 * detprop->Eloss(p, mass, getTcut());
    double range = t / dedx;
    if(range > 100.)
      range = 100.;

    // Calculate the radiation length in cm.

    double x0 = larprop->RadiationLength() / detprop->Density();

    // Calculate projected rms scattering angle.
    // Use the estimted range in the logarithm factor.
    // Use the incremental propagation distance in the square root factor.

    double betainv = std::sqrt(1. + pinv*pinv * mass*mass);
    double theta_fact = (0.0136 * pinv * betainv) * (1. + 0.038 * std::log(range/x0));
    double theta02 = theta_fact*theta_fact * std::abs(s/x0);

    // Calculate some sommon factors needed for multiple scattering.

    double ufact2 = 1. + dudw*dudw;
    double vfact2 = 1. + dvdw*dvdw;
    double uvfact2 = 1. + dudw*dudw + dvdw*dvdw;
    double uvfact = std::sqrt(uvfact2);
    double uv = dudw * dvdw;
    double dist2_3 = s*s / 3.;
    double dist_2 = std::abs(s) / 2.;
    if(trk.getDirection() == Surface::BACKWARD)
      dist_2 = -dist_2;

    // Calculate energy loss fluctuations.

    double evar = 1.e-6 * detprop->ElossVar(p, mass) * std::abs(s); // E variance (GeV^2).
    double pinvvar = evar * e2 / (p2*p2*p2);                        // Inv. p variance (1/GeV^2)

    // Fill elements of noise matrix.

    // Position submatrix.

    noise_matrix(0,0) = dist2_3 * theta02 * ufact2;           // sigma^2(u,u)
    noise_matrix(1,0) = dist2_3 * theta02 * uv;               // sigma^2(u,v)
    noise_matrix(1,1) = dist2_3 * theta02 * vfact2;           // sigma^2(v,v)

    // Slope submatrix.

    noise_matrix(2,2) = theta02 * uvfact2 * ufact2;           // sigma^2(u', u')
    noise_matrix(3,2) = theta02 * uvfact2 * uv;               // sigma^2(v', u')
    noise_matrix(3,3) = theta02 * uvfact2 * vfact2;           // sigma^2(v', v')

    // Same-view position-slope correlations.

    noise_matrix(2,0) = dist_2 * theta02 * uvfact * ufact2;   // sigma^2(u', u)
    noise_matrix(3,1) = dist_2 * theta02 * uvfact * vfact2;   // sigma^2(v', v)

    // Opposite-view position-slope correlations.

    noise_matrix(2,1) = dist_2 * theta02 * uvfact * uv;       // sigma^2(u', v)
    noise_matrix(3,0) = dist_2 * theta02 * uvfact * uv;       // sigma^2(v', u)

    // Momentum correlations (zero).

    noise_matrix(4,0) = 0.;                                   // sigma^2(pinv, u)
    noise_matrix(4,1) = 0.;                                   // sigma^2(pinv, v)
    noise_matrix(4,2) = 0.;                                   // sigma^2(pinv, u')
    noise_matrix(4,3) = 0.;                                   // sigma^2(pinv, v')

    // Energy loss fluctuations.

    noise_matrix(4,4) = pinvvar;                              // sigma^2(pinv, pinv)

    // Done (success).

    return true;
  }

---

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

• /cvmfs/larsoft.opensciencegrid.org/products/lardata/v07_01_01/source/lardata/RecoObjects/InteractPlane.h
• /cvmfs/larsoft.opensciencegrid.org/products/lardata/v07_01_01/source/lardata/RecoObjects/InteractPlane.cxx