Analysis Software
Documentation for sPHENIX simulation software
 All Classes Namespaces Files Functions Variables Typedefs Enumerations Enumerator Friends Macros Groups Pages
HelixTrackModel.cc
Go to the documentation of this file. Or view the newest version in sPHENIX GitHub for file HelixTrackModel.cc
1 /* Copyright 2008-2010, Technische Universitaet Muenchen,
2  Authors: Christian Hoeppner & Sebastian Neubert & Johannes Rauch
3 
4  This file is part of GENFIT.
5 
6  GENFIT is free software: you can redistribute it and/or modify
7  it under the terms of the GNU Lesser General Public License as published
8  by the Free Software Foundation, either version 3 of the License, or
9  (at your option) any later version.
10 
11  GENFIT is distributed in the hope that it will be useful,
12  but WITHOUT ANY WARRANTY; without even the implied warranty of
13  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14  GNU Lesser General Public License for more details.
15 
16  You should have received a copy of the GNU Lesser General Public License
17  along with GENFIT. If not, see <http://www.gnu.org/licenses/>.
18 */
19 
20 #include "HelixTrackModel.h"
21 #include <FieldManager.h>
22 
23 #include <assert.h>
24 #include <math.h>
25 
26 namespace genfit {
27 
28 HelixTrackModel::HelixTrackModel(const TVector3& pos, const TVector3& mom, double charge) {
29 
30  mom_ = mom.Mag();
31 
32  TVector3 B = genfit::FieldManager::getInstance()->getFieldVal(pos);
33 
34  // B must point in Z direction
35  assert(B.X() == 0);
36  assert(B.Y() == 0);
37 
38  double Bz = B.Z();
39 
40  // calc helix parameters
41  TVector3 dir2D(mom);
42  dir2D.SetZ(0);
43  dir2D.SetMag(1.);
44  R_ = 100.*mom.Perp()/(0.0299792458*Bz) / fabs(charge);
45  sgn_ = 1;
46  if (charge<0) sgn_=-1.;
47  center_ = pos + sgn_ * R_ * dir2D.Orthogonal();
48  alpha0_ = (pos-center_).Phi();
49 
50  theta_ = mom.Theta();
51 
52  //std::cout<<"radius " << R_ << " center ";
53  //center_.Print();
54 
55 }
56 
57 
58 TVector3 HelixTrackModel::getPos(double tracklength) const {
59 
60  TVector3 pos;
61 
62  double angle = alpha0_ - sgn_ * tracklength / R_ * sin(theta_);
63 
64  TVector3 radius(R_,0,0);
65  radius.SetPhi(angle);
66  pos = center_ + radius;
67  pos.SetZ(center_.Z() - sgn_ * ((alpha0_-angle)*R_ * tan(theta_-M_PI/2.)) );
68 
69  return pos;
70 }
71 
72 void HelixTrackModel::getPosMom(double tracklength, TVector3& pos, TVector3& mom) const {
73 
74  double angle = alpha0_ - sgn_ * tracklength / R_ * sin(theta_);
75 
76  TVector3 radius(R_,0,0);
77  radius.SetPhi(angle);
78  pos = center_ + radius;
79  pos.SetZ(center_.Z() - sgn_ * ((alpha0_-angle)*R_ * tan(theta_-M_PI/2.)) );
80 
81  mom.SetXYZ(1,1,1);
82  mom.SetTheta(theta_);
83  mom.SetPhi(angle - sgn_*M_PI/2.);
84  mom.SetMag(mom_);
85 
86  /*std::cout<<"tracklength " << tracklength << "\n";
87  std::cout<<"angle " << angle << "\n";
88  std::cout<<"radius vector "; radius.Print();
89  std::cout<<"pos "; pos.Print();
90  std::cout<<"mom "; mom.Print();*/
91 
92 }
93 
94 
95 } /* End of namespace genfit */