GFGbl.cc File Reference

#include "GFGbl.h"
#include "GblTrajectory.h"
#include "GblPoint.h"
#include "MyDebugTools.h"
#include "AbsMeasurement.h"
#include "PlanarMeasurement.h"
#include "KalmanFitterInfo.h"
#include "Track.h"
#include <TFile.h>
#include <TH1F.h>
#include <TTree.h>
#include <string>
#include <list>
#include <FieldManager.h>
#include <HMatrixU.h>
#include <HMatrixV.h>
#include <Math/SMatrix.h>
#include <TMatrixD.h>
#include <TVectorDfwd.h>
#include <TMatrixT.h>
#include <TVector3.h>

Include dependency graph for GFGbl.cc:

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Functions
void	getScattererFromMatList (double &length, double &theta, double &s, double &ds, const double p, const double mass, const double charge, const std::vector< MatStep > &steps)
	Evaluates moments of radiation length distribution from list of material steps and computes parameters describing a corresponding thick scatterer.

Variables
gbl::MilleBinary *	milleFile
const double	scatEpsilon = 1.e-8

Function Documentation

getScattererFromMatList()

void getScattererFromMatList	(	double &	length,
		double &	theta,
		double &	s,
		double &	ds,
		const double	p,
		const double	mass,
		const double	charge,
		const std::vector< MatStep > &	steps
	)

Evaluates moments of radiation length distribution from list of material steps and computes parameters describing a corresponding thick scatterer.

Based on input from Claus Kleinwort (DESY), adapted for continuous material distribution represented by a sum of step functions. Returned thick scatterer can be represented by two GBL scattering points at (s - ds) and (s + ds) with variance of theta equal to theta/sqrt(2) for both points. Calculates variance of theta from total sum of radiation lengths instead of summimg squares of individual deflection angle variances.

Parameters

length	returned: Length of the track
theta	returned: Variation of distribution of deflection angle
s	returned: First moment of material scattering distribution
ds	returned: Second moment (variance) of material scattering distribution
p	Particle momentum magnitude (GeV/c)
mass	Mass of particle (GeV/c/c)
steps	Vector of material steps from (RKTrackRep) extrapolation

Returns

void

Definition at line 262 of file GFGbl.cc.

{
  theta = 0.; s = 0.; ds = 0.;
  if (steps.empty()) return;
 
  // sum of step lengths
  double len = 0.;
  // normalization
  double sumxx = 0.;
  // first moment (non-normalized)
  double sumx2x2 = 0.;
  // (part of) second moment / variance (non-normalized)
  double sumx3x3 = 0.;
 
  double xmin = 0.;
  double xmax = 0.;
 
  for (unsigned int i = 0; i < steps.size(); i++) {
    const MatStep step = steps.at(i);
    // inverse of material radiation length ... (in 1/cm) ... "density of scattering"
    double rho = 1. / step.materialProperties_.getRadLen();
    len += fabs(step.stepSize_);
    xmin = xmax;
    xmax = xmin + fabs(step.stepSize_);
    // Compute integrals
 
    // integral of rho(x)
    sumxx   += rho * (xmax - xmin);
    // integral of x*rho(x)
    sumx2x2 += rho * (xmax * xmax - xmin * xmin) / 2.;
    // integral of x*x*rho(x)
    sumx3x3 += rho * (xmax * xmax * xmax - xmin * xmin * xmin) / 3.;
  }
  // This ensures PDG formula still gives positive results (but sumxx should be > 1e-4 for it to hold)
  if (sumxx < 1.0e-10) return;
  // Calculate theta from total sum of radiation length
  // instead of summimg squares of individual deflection angle variances
  // PDG formula:
  double beta = p / sqrt(p * p + mass * mass);
  theta = (0.0136 / p / beta) * fabs(charge) * sqrt(sumxx) * (1. + 0.038 * log(sumxx));
  //theta = (0.015 / p / beta) * fabs(charge) * sqrt(sumxx);
 
  // track length
  length = len;
  // Normalization factor
  double N = 1. / sumxx;
  // First moment
  s  = N * sumx2x2;
  // Square of second moment (variance)
  // integral of (x - s)*(x - s)*rho(x)
  double ds_2 = N * (sumx3x3 - 2. * sumx2x2 * s + sumxx * s * s);
  ds = sqrt(ds_2);
 
  #ifdef DEBUG
  //cout << "Thick scatterer parameters:" << endl;
  //cout << "Variance of theta: " << theta << endl;
  //cout << "Mean s           : " << s << endl;
  //cout << "Variance of s    : " << ds << endl;
 
  #endif
}

Variable Documentation

milleFile

gbl::MilleBinary* milleFile

Definition at line 166 of file GFGbl.cc.

scatEpsilon

const double scatEpsilon = 1.e-8

Definition at line 168 of file GFGbl.cc.