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da0e9ce3 | 1 | //-------------------------------------------------------------------------- |
2 | // | |
3 | // Environment: | |
4 | // This software is part of the EvtGen package developed jointly | |
5 | // for the BaBar and CLEO collaborations. If you use all or part | |
6 | // of it, please give an appropriate acknowledgement. | |
7 | // | |
8 | // Copyright Information: See EvtGen/COPYRIGHT | |
9 | // Copyright (C) 1998 Caltech, UCSB | |
10 | // | |
11 | // Module: EvtSemiLeptonicAmp.cc | |
12 | // | |
13 | // Description: Base class for semileptonic decays | |
14 | // | |
15 | // Modification history: | |
16 | // | |
17 | // DJL April 17,1998 Module created | |
18 | // | |
19 | //------------------------------------------------------------------------ | |
20 | // | |
21 | #include "EvtGenBase/EvtPatches.hh" | |
22 | #include "EvtGenBase/EvtPatches.hh" | |
23 | #include "EvtGenBase/EvtParticle.hh" | |
24 | #include "EvtGenBase/EvtGenKine.hh" | |
25 | #include "EvtGenBase/EvtPDL.hh" | |
26 | #include "EvtGenBase/EvtReport.hh" | |
27 | #include "EvtGenBase/EvtVector4C.hh" | |
28 | #include "EvtGenBase/EvtTensor4C.hh" | |
29 | #include "EvtGenBase/EvtDiracSpinor.hh" | |
30 | #include "EvtGenBase/EvtSemiLeptonicScalarAmp.hh" | |
31 | #include "EvtGenBase/EvtId.hh" | |
32 | #include "EvtGenBase/EvtAmp.hh" | |
33 | #include "EvtGenBase/EvtScalarParticle.hh" | |
34 | #include "EvtGenBase/EvtVectorParticle.hh" | |
35 | #include "EvtGenBase/EvtTensorParticle.hh" | |
36 | ||
37 | double EvtSemiLeptonicAmp::CalcMaxProb( EvtId parent, EvtId meson, | |
38 | EvtId lepton, EvtId nudaug, | |
39 | EvtSemiLeptonicFF *FormFactors ) { | |
40 | ||
41 | //This routine takes the arguements parent, meson, and lepton | |
42 | //number, and a form factor model, and returns a maximum | |
43 | //probability for this semileptonic form factor model. A | |
44 | //brute force method is used. The 2D cos theta lepton and | |
45 | //q2 phase space is probed. | |
46 | ||
47 | //Start by declaring a particle at rest. | |
48 | ||
49 | //It only makes sense to have a scalar parent. For now. | |
50 | //This should be generalized later. | |
51 | ||
52 | EvtScalarParticle *scalar_part; | |
53 | EvtParticle *root_part; | |
54 | ||
55 | scalar_part=new EvtScalarParticle; | |
56 | ||
57 | //cludge to avoid generating random numbers! | |
58 | scalar_part->noLifeTime(); | |
59 | ||
60 | EvtVector4R p_init; | |
61 | ||
62 | p_init.set(EvtPDL::getMass(parent),0.0,0.0,0.0); | |
63 | scalar_part->init(parent,p_init); | |
64 | root_part=(EvtParticle *)scalar_part; | |
65 | root_part->setDiagonalSpinDensity(); | |
66 | ||
67 | EvtParticle *daughter, *lep, *trino; | |
68 | ||
69 | EvtAmp amp; | |
70 | ||
71 | EvtId listdaug[3]; | |
72 | listdaug[0] = meson; | |
73 | listdaug[1] = lepton; | |
74 | listdaug[2] = nudaug; | |
75 | ||
76 | amp.init(parent,3,listdaug); | |
77 | ||
78 | root_part->makeDaughters(3,listdaug); | |
79 | daughter=root_part->getDaug(0); | |
80 | lep=root_part->getDaug(1); | |
81 | trino=root_part->getDaug(2); | |
82 | ||
83 | //cludge to avoid generating random numbers! | |
84 | daughter->noLifeTime(); | |
85 | lep->noLifeTime(); | |
86 | trino->noLifeTime(); | |
87 | ||
88 | ||
89 | //Initial particle is unpolarized, well it is a scalar so it is | |
90 | //trivial | |
91 | EvtSpinDensity rho; | |
92 | rho.setDiag(root_part->getSpinStates()); | |
93 | ||
94 | double mass[3]; | |
95 | ||
96 | double m = root_part->mass(); | |
97 | ||
98 | EvtVector4R p4meson, p4lepton, p4nu, p4w; | |
99 | double q2max; | |
100 | ||
101 | double q2, elepton, plepton; | |
102 | int i,j; | |
103 | double erho,prho,costl; | |
104 | ||
105 | double maxfoundprob = 0.0; | |
106 | double prob = -10.0; | |
107 | int massiter; | |
108 | ||
109 | for (massiter=0;massiter<3;massiter++){ | |
110 | ||
111 | mass[0] = EvtPDL::getMeanMass(meson); | |
112 | mass[1] = EvtPDL::getMeanMass(lepton); | |
113 | mass[2] = EvtPDL::getMeanMass(nudaug); | |
114 | if ( massiter==1 ) { | |
115 | mass[0] = EvtPDL::getMinMass(meson); | |
116 | } | |
117 | if ( massiter==2 ) { | |
118 | mass[0] = EvtPDL::getMaxMass(meson); | |
119 | if ( (mass[0]+mass[1]+mass[2])>m) mass[0]=m-mass[1]-mass[2]-0.00001; | |
120 | } | |
121 | ||
122 | q2max = (m-mass[0])*(m-mass[0]); | |
123 | ||
124 | //loop over q2 | |
125 | ||
126 | for (i=0;i<25;i++) { | |
127 | q2 = ((i+0.5)*q2max)/25.0; | |
128 | ||
129 | erho = ( m*m + mass[0]*mass[0] - q2 )/(2.0*m); | |
130 | ||
131 | prho = sqrt(erho*erho-mass[0]*mass[0]); | |
132 | ||
133 | p4meson.set(erho,0.0,0.0,-1.0*prho); | |
134 | p4w.set(m-erho,0.0,0.0,prho); | |
135 | ||
136 | //This is in the W rest frame | |
137 | elepton = (q2+mass[1]*mass[1])/(2.0*sqrt(q2)); | |
138 | plepton = sqrt(elepton*elepton-mass[1]*mass[1]); | |
139 | ||
140 | double probctl[3]; | |
141 | ||
142 | for (j=0;j<3;j++) { | |
143 | ||
144 | costl = 0.99*(j - 1.0); | |
145 | ||
146 | //These are in the W rest frame. Need to boost out into | |
147 | //the B frame. | |
148 | p4lepton.set(elepton,0.0, | |
149 | plepton*sqrt(1.0-costl*costl),plepton*costl); | |
150 | p4nu.set(plepton,0.0, | |
151 | -1.0*plepton*sqrt(1.0-costl*costl),-1.0*plepton*costl); | |
152 | ||
153 | EvtVector4R boost((m-erho),0.0,0.0,1.0*prho); | |
154 | p4lepton=boostTo(p4lepton,boost); | |
155 | p4nu=boostTo(p4nu,boost); | |
156 | ||
157 | //Now initialize the daughters... | |
158 | ||
159 | daughter->init(meson,p4meson); | |
160 | lep->init(lepton,p4lepton); | |
161 | trino->init(nudaug,p4nu); | |
162 | ||
163 | CalcAmp(root_part,amp,FormFactors); | |
164 | ||
165 | //Now find the probability at this q2 and cos theta lepton point | |
166 | //and compare to maxfoundprob. | |
167 | ||
168 | //Do a little magic to get the probability!! | |
169 | prob = rho.normalizedProb(amp.getSpinDensity()); | |
170 | ||
171 | probctl[j]=prob; | |
172 | } | |
173 | ||
174 | //probclt contains prob at ctl=-1,0,1. | |
175 | //prob=a+b*ctl+c*ctl^2 | |
176 | ||
177 | double a=probctl[1]; | |
178 | double b=0.5*(probctl[2]-probctl[0]); | |
179 | double c=0.5*(probctl[2]+probctl[0])-probctl[1]; | |
180 | ||
181 | prob=probctl[0]; | |
182 | if (probctl[1]>prob) prob=probctl[1]; | |
183 | if (probctl[2]>prob) prob=probctl[2]; | |
184 | ||
185 | if (fabs(c)>1e-20){ | |
186 | double ctlx=-0.5*b/c; | |
187 | if (fabs(ctlx)<1.0){ | |
188 | double probtmp=a+b*ctlx+c*ctlx*ctlx; | |
189 | if (probtmp>prob) prob=probtmp; | |
190 | } | |
191 | ||
192 | } | |
193 | ||
194 | if ( prob > maxfoundprob ) { | |
195 | maxfoundprob = prob; | |
196 | } | |
197 | ||
198 | } | |
199 | if ( EvtPDL::getWidth(meson) <= 0.0 ) { | |
200 | //if the particle is narrow dont bother with changing the mass. | |
201 | massiter = 4; | |
202 | } | |
203 | ||
204 | } | |
205 | root_part->deleteTree(); | |
206 | ||
207 | maxfoundprob *=1.1; | |
208 | return maxfoundprob; | |
209 | ||
210 | } | |
211 |