1 package org.lcsim.recon.tracking.trfcyl;
2
3 import org.lcsim.recon.tracking.trfutil.Assert;
4 import org.lcsim.recon.tracking.trfbase.SimInteractor;
5 import org.lcsim.recon.tracking.trfbase.VTrack;
6 import org.lcsim.recon.tracking.trfbase.TrackVector;
7 import org.lcsim.recon.tracking.trfeloss.DeDx;
8
9
10 /**
11 * Class for simulating Energy Loss in SurfCylinders.
12 *
13 *@author Norman A. Graf
14 *@version 1.0
15 *
16 */
17 public class CylElossSim extends SimInteractor
18 {
19
20 //attributes
21 //thickness of the material in the cylinder
22 private double _thickness;
23 // type of energy loss being simulated
24 private DeDx _dedx;
25
26 //
27
28 /**
29 *Construct in instance with the
30 *appropriate thickness and DeDx class to model
31 *
32 *
33 * @param thickness Thickness of the cylindrical shell.
34 * @param dedx The DeDx class representing energy loss.
35 */
36 public CylElossSim(double thickness, DeDx dedx)
37 {
38 _thickness = thickness;
39 _dedx = dedx;
40 }
41
42 //
43
44 /**
45 *Construct an instance from a CylEloss Interactor.
46 *
47 * @param inter The CylEloss Interactor to use for simulation.
48 */
49 public CylElossSim(CylEloss inter)
50 {
51 _thickness = inter.thickness();
52 _dedx = inter.dEdX();
53 }
54
55 //
56
57 /**
58 *Interact the given track in this cylindrical shell,
59 *using the DeDx model for energy loss.
60 *Note that the track parameters are updated to reflect the
61 *energy lost by traversing the cylindrical shell of material.
62 *
63 * @param vtrk The VTrack to scatter.
64 */
65 public void interact( VTrack vtrk )
66 {
67 // This can only be used with cylinders... check that we have one..
68
69 Assert.assertTrue( vtrk.surface() instanceof SurfCylinder );
70
71
72 TrackVector theVec = vtrk.vector();
73 TrackVector newVector = new TrackVector(theVec);
74
75 double pionMass = 0.13957; // GeV
76 double ptmax = 10000.; // GeV
77
78 double pinv = Math.abs(theVec.get(SurfCylinder.IQPT)*Math.cos(Math.atan(theVec.get(SurfCylinder.ITLM))));
79
80 // make sure pinv is greater than a threshold (1/ptmax)
81 // in this case assume q = 1, otherwise q = q/pt/abs(q/pt)
82
83 double sign = 1;
84 if(pinv < 1./ptmax)
85 pinv = 1./ptmax;
86 else
87 sign = theVec.get(SurfCylinder.IQPT)/Math.abs(theVec.get(SurfCylinder.IQPT));
88
89 // Evaluate the initial energy assuming the particle is a pion.
90
91 double trackEnergy = Math.sqrt(1./pinv/pinv+pionMass*pionMass);
92
93 double trueLength = _thickness/Math.abs(Math.cos(theVec.get(SurfCylinder.IALF)))/
94 Math.cos(Math.atan(theVec.get(SurfCylinder.ITLM)));
95 // assume the energy loss distribution to be Gaussian
96 double stdEnergy = _dedx.sigmaEnergy(trackEnergy, trueLength);
97 double stdMomentum = stdEnergy;
98 // What direction are we going?
99 // If forward, that means we lose energy
100 // backwards means gain energy
101
102 if(vtrk.isTrackForward()) trueLength = -trueLength;
103 trackEnergy=_dedx.loseEnergy(trackEnergy, trueLength);
104 double newMomentum = trackEnergy>pionMass ?
105 Math.sqrt(trackEnergy*trackEnergy-
106 pionMass*pionMass): 1./pinv;
107 // Only vec(SurfCylinder.IQPT) changes due to E loss.
108 newVector.set(SurfCylinder.IQPT, 1./newMomentum/Math.cos(Math.atan(theVec.get(SurfCylinder.ITLM)))*sign);
109 vtrk.setVectorAndKeepDirection(newVector);
110
111 }
112 //
113
114 /**
115 *Return the thickness of material in the cylindrical shell.
116 *
117 * @return The thickness of the energy loss material.
118 */
119 public double thickness()
120 { return _thickness;
121 }
122 //
123
124 /**
125 *Return the energy loss model used in this Interactor.
126 *
127 * @return The DeDx class representing energy loss.
128 */
129 public DeDx dEdX()
130 {
131 return _dedx; //cng shallow copy!
132 }
133
134 //
135
136 /**
137 *Make a clone of this object.
138 * Note that new copy will have different random number generator.
139 *
140 * @return A Clone of this instance.
141 */
142 public SimInteractor newCopy()
143 {
144 return new CylElossSim(_thickness,_dedx);
145 }
146
147
148 /**
149 *output stream
150 *
151 * @return A String representation of this instance.
152 */
153 public String toString()
154 {
155 return "CylElossSim with thickness "+_thickness+" and energy loss "+_dedx;
156 }
157 }