trackingParametersAtClosestApproachToBeamSpot.cc

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// -*- C++ -*-
//
// Package:     TrackingTools/PatternTools
// Class  :     trackingParametersAtClosestApproachToBeamSpot
//
// Implementation:
//     [Notes on implementation]
//
// Original Author:  Christopher Jones
//         Created:  Fri, 02 Jan 2015 19:32:37 GMT
//

// system include files

// user include files
#include "TrackingTools/PatternTools/interface/trackingParametersAtClosestApproachToBeamSpot.h"
#include "TrackingTools/TrajectoryState/interface/FreeTrajectoryState.h"
#include "TrackingTools/PatternTools/interface/TSCBLBuilderNoMaterial.h"
#include "DataFormats/GeometryVector/interface/Pi.h"

std::pair<bool, reco::TrackBase::ParameterVector> reco::trackingParametersAtClosestApproachToBeamSpot(
    const Basic3DVector<double>& vertex,
    const Basic3DVector<double>& momAtVtx,
    float charge,
    const MagneticField& magField,
    const BeamSpot& bs) {
  TrackBase::ParameterVector sParameters;
  try {
    FreeTrajectoryState ftsAtProduction(GlobalPoint(vertex.x(), vertex.y(), vertex.z()),
                                        GlobalVector(momAtVtx.x(), momAtVtx.y(), momAtVtx.z()),
                                        TrackCharge(charge),
                                        &magField);
    TSCBLBuilderNoMaterial tscblBuilder;
    TrajectoryStateClosestToBeamLine tsAtClosestApproach =
        tscblBuilder(ftsAtProduction, bs);  //as in TrackProducerAlgorithm

    GlobalPoint v = tsAtClosestApproach.trackStateAtPCA().position();
    GlobalVector p = tsAtClosestApproach.trackStateAtPCA().momentum();
    sParameters[0] = tsAtClosestApproach.trackStateAtPCA().charge() / p.mag();
    sParameters[1] = Geom::halfPi() - p.theta();
    sParameters[2] = p.phi();
    sParameters[3] = (-v.x() * sin(p.phi()) + v.y() * cos(p.phi()));
    sParameters[4] = v.z() * p.perp() / p.mag() - (v.x() * p.x() + v.y() * p.y()) / p.perp() * p.z() / p.mag();

    return std::make_pair(true, sParameters);
  } catch (cms::Exception const&) {
    return std::make_pair(false, sParameters);
  }
}