Line data Source code
1 : /**************************************************************************
2 : * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
3 : * *
4 : * Author: The ALICE Off-line Project. *
5 : * Contributors are mentioned in the code where appropriate. *
6 : * *
7 : * Permission to use, copy, modify and distribute this software and its *
8 : * documentation strictly for non-commercial purposes is hereby granted *
9 : * without fee, provided that the above copyright notice appears in all *
10 : * copies and that both the copyright notice and this permission notice *
11 : * appear in the supporting documentation. The authors make no claims *
12 : * about the suitability of this software for any purpose. It is *
13 : * provided "as is" without express or implied warranty. *
14 : **************************************************************************/
15 :
16 : #include <TMath.h>
17 : #include <TF1.h>
18 : #include <TDatabasePDG.h>
19 : #include <TParticlePDG.h>
20 : #include <TParticle.h>
21 : #include <TVector3.h>
22 : #include <TRandom.h>
23 : #include <TObjectTable.h>
24 :
25 : #include "AliDecayerPolarized.h"
26 : #include "AliLog.h"
27 :
28 6 : ClassImp(AliDecayerPolarized)
29 :
30 :
31 :
32 : //____________________________________________________________
33 0 : AliDecayerPolarized::AliDecayerPolarized():
34 0 : fAlpha(0),
35 0 : fSystRef(kHelicity),
36 0 : fDecProd(kMuon),
37 0 : fPol(0),
38 0 : fMother(0),
39 0 : fDaughter1(0),
40 0 : fDaughter2(0)
41 0 : {
42 : // Default constructor
43 :
44 0 : }
45 :
46 : //____________________________________________________________
47 0 : AliDecayerPolarized::AliDecayerPolarized(Double_t alpha, Polar_t systref, FinState_t decprod):
48 0 : fAlpha(alpha),
49 0 : fSystRef(systref),
50 0 : fDecProd(decprod),
51 0 : fPol(new TF1("dsigdcostheta","1.+[0]*x*x",-1.,1.)),
52 0 : fMother(0),
53 0 : fDaughter1(0),
54 0 : fDaughter2(0)
55 0 : {
56 : // Another constructor
57 0 : fPol->SetParameter(0,fAlpha);
58 0 : if(fDecProd!=kMuon && fDecProd!=kElectron)
59 0 : AliFatal("Only polarized decay into muons or electrons is implemented!");
60 0 : }
61 :
62 : AliDecayerPolarized::AliDecayerPolarized(const AliDecayerPolarized &decayer):
63 0 : AliDecayer(decayer),
64 0 : fAlpha(0),
65 0 : fSystRef(kHelicity),
66 0 : fDecProd(kMuon),
67 0 : fPol(new TF1("dsigdcostheta","1.+[0]*x*x",-1.,1.)),
68 0 : fMother(0),
69 0 : fDaughter1(0),
70 0 : fDaughter2(0)
71 0 : {
72 : // Copy Constructor
73 0 : decayer.Copy(*this);
74 0 : }
75 :
76 : //____________________________________________________________
77 : AliDecayerPolarized::~AliDecayerPolarized()
78 0 : {
79 : // Destructor
80 0 : delete fPol;
81 0 : delete fMother;
82 0 : delete fDaughter1;
83 0 : delete fDaughter2;
84 0 : }
85 : //____________________________________________________________
86 : void AliDecayerPolarized::Decay(Int_t ipart, TLorentzVector *p)
87 : {
88 : // Polarized 2- body decay
89 0 : TDatabasePDG *pDataBase = TDatabasePDG::Instance();
90 0 : if(ipart!= (pDataBase->GetParticle("J/psi")->PdgCode()) &&
91 0 : ipart!= (pDataBase->GetParticle("psi'")->PdgCode()) &&
92 0 : ipart!= (pDataBase->GetParticle("Upsilon")->PdgCode()) &&
93 0 : ipart!= (pDataBase->GetParticle("Upsilon'")->PdgCode()))
94 0 : AliFatal("Polarized decay only implemented for J/psi, psi', Upsilon and Upsilon' !");
95 :
96 : TParticlePDG *d1 = 0, *d2 = 0;
97 0 : if(fDecProd==kMuon){
98 0 : d1 = pDataBase->GetParticle("mu-");
99 0 : d2 = pDataBase->GetParticle("mu+");
100 0 : }
101 0 : else if(fDecProd==kElectron){
102 0 : d1 = pDataBase->GetParticle("e-");
103 0 : d2 = pDataBase->GetParticle("e+");
104 0 : }
105 : // energies and momenta in lab frame
106 0 : Double_t e1 = p->M() / 2.;
107 : Double_t e2 = e1;
108 0 : Double_t p1 = TMath::Sqrt((e1 + d1->Mass())*(e1 - d1->Mass()));
109 :
110 0 : Double_t costheta = fPol->GetRandom();
111 :
112 0 : Double_t sintheta = TMath::Sqrt((1. + costheta)*(1. - costheta));
113 0 : Double_t phi = 2. * TMath::Pi() * gRandom->Rndm();
114 0 : Double_t px1 = p1 * sintheta * TMath::Cos(phi);
115 0 : Double_t py1 = p1 * sintheta * TMath::Sin(phi);
116 0 : Double_t pz1 = p1 * costheta;
117 :
118 0 : TLorentzVector v1,v2, boosted1, boosted2;
119 0 : v1.SetPxPyPzE(-px1,-py1,-pz1,e1); //in the dimuon rest frame
120 0 : v2.SetPxPyPzE(px1,py1,pz1,e2);
121 :
122 0 : TLorentzVector pProj, pTarg; // In the CM frame
123 : Float_t mp = 0.938;
124 0 : pProj.SetPxPyPzE(0.,0.,-7000.,TMath::Sqrt(7000.*7000.+mp*mp)); // projectile
125 0 : pTarg.SetPxPyPzE(0.,0.,7000.,TMath::Sqrt(7000.*7000.+mp*mp)); // target
126 :
127 0 : TVector3 betajpsicm;
128 0 : betajpsicm = (-1./p->E()*p->Vect());
129 :
130 0 : if(fSystRef == kHelicity) {
131 : // polarization axis: direction of the JPsi in the CM
132 0 : TVector3 v3jpsi = (p->Vect()).Unit();
133 0 : v1.RotateUz(v3jpsi);
134 0 : v2.RotateUz(v3jpsi);
135 0 : } else if (fSystRef == kColSop){
136 : // polarization axis: bisector of proj and target in the dimuon rest frame
137 0 : pProj.Boost(betajpsicm); //boost proj and targ from CM to DIMU rest frame
138 0 : pTarg.Boost(betajpsicm);
139 :
140 0 : TVector3 zaxisCS;
141 0 : zaxisCS=(((pProj.Vect()).Unit())-((pTarg.Vect()).Unit())).Unit();
142 0 : v1.RotateUz(zaxisCS);
143 0 : v2.RotateUz(zaxisCS);
144 0 : }
145 :
146 : // printf("v1 components (mu1 with jpsi at rest)%f %f %f %f\n",v1.Px(),v1.Py(),v1.Pz(),v1.E());
147 : // printf("v2 components (mu2 with jpsi at rest)%f %f %f %f\n",v2.Px(),v2.Py(),v2.Pz(),v2.E());
148 :
149 0 : v1.Boost(-betajpsicm); //boost muons from DIMUON rest frame to CM
150 0 : v2.Boost(-betajpsicm);
151 :
152 : // printf("v1 components (mu1 in polar. ref. syst.) %f %f %f %f\n",v1.Px(),v1.Py(),v1.Pz(),v1.E());
153 : // printf("v2 components (mu2 in polar. ref. syst.) %f %f %f %f\n",v2.Px(),v2.Py(),v2.Pz(),v2.E());
154 :
155 : Int_t statusDecayed=11;
156 : Int_t statusUndecayed=1;
157 :
158 :
159 0 : fMother = new TParticle(ipart,statusDecayed,0,-1,2,3,p->Px(),p->Py(),p->Pz(),p->E(),0.,0.,0.,0);
160 0 : fDaughter1 = new TParticle(d1->PdgCode(),statusUndecayed,1,-1,0,0,v1.Px(),v1.Py(),v1.Pz(),v1.E(),0.,0.,0.,0);
161 0 : fDaughter2 = new TParticle(d2->PdgCode(),statusUndecayed,1,-1,0,0,v2.Px(),v2.Py(),v2.Pz(),v2.E(),0.,0.,0.,0);
162 :
163 0 : }
164 :
165 : //____________________________________________________________
166 : Int_t AliDecayerPolarized::ImportParticles(TClonesArray *part)
167 : {
168 : // Return array of particles
169 : TClonesArray &cloneparticles = *part;
170 0 : cloneparticles.Clear();
171 :
172 0 : new(cloneparticles[0])TParticle(*fMother);
173 0 : new(cloneparticles[1])TParticle(*fDaughter1);
174 0 : new(cloneparticles[2])TParticle(*fDaughter2);
175 :
176 0 : return part->GetEntries();
177 0 : }
178 :
179 : void AliDecayerPolarized::Copy(TObject &) const
180 : {
181 : //
182 : // Copy *this onto AliDecayerPolarized -- not implemented
183 : //
184 0 : Fatal("Copy","Not implemented!\n");
185 0 : }
186 :
187 : void AliDecayerPolarized::SetForceDecay(Int_t)
188 : {
189 : // This method is dummy
190 0 : }
191 :
192 : void AliDecayerPolarized::ForceDecay()
193 : {
194 : // This method is dummy
195 0 : AliWarning("Method not implemented for this class !\n");
196 0 : }
197 :
198 : Float_t AliDecayerPolarized::GetPartialBranchingRatio(Int_t)
199 : {
200 : // This method is dummy
201 0 : return 1.;
202 : }
203 :
204 : Float_t AliDecayerPolarized::GetLifetime(Int_t)
205 : {
206 : // This method is dummy
207 0 : AliWarning("Method not implemented for this class !\n");
208 0 : return -1.;
209 : }
210 :
211 : void AliDecayerPolarized::ReadDecayTable()
212 : {
213 : // This method is dummy
214 0 : AliWarning("Method not implemented for this class !\n");
215 0 : }
216 :
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