Fix for event mixing, when it was selecting events out of range of multiplicity cut
[u/mrichter/AliRoot.git] / EVGEN / AliOmegaDalitz.cxx
CommitLineData
8c90f5a2 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
17/* $Id$ */
18
19
20#include "AliOmegaDalitz.h"
21#include <TMath.h>
22#include <AliLog.h>
23#include <TH1.h>
24#include <TPDGCode.h>
25#include <TRandom.h>
26#include <TParticle.h>
27#include <TDatabasePDG.h>
28#include <TLorentzVector.h>
29#include <TClonesArray.h>
30
31ClassImp(AliOmegaDalitz)
32
33
34//-----------------------------------------------------------------------------
35//
36// Generate lepton-pair mass distributions for Dalitz decays according
37// to the Kroll-Wada parametrization: N. Kroll, W. Wada: Phys. Rev 98(1955)1355
38//
39// For the electromagnetic form factor the parameterization from
40// Lepton-G is used: L.G. Landsberg et al.: Phys. Rep. 128(1985)301
41//
42//-----------------------------------------------------------------------------
43//
44// Adaption for AliRoot
45//
46// R. Averbeck
47// A. Morsch
48//
49AliOmegaDalitz::AliOmegaDalitz():
50 AliDecayer(),
0439b2b7 51 fEPMass(0),
52 fMPMass(0)
8c90f5a2 53{
54 // Constructor
55}
56
57void AliOmegaDalitz::Init()
58{
59 // Initialisation
0439b2b7 60 Int_t idecay, ibin, nbins = 1000;
8c90f5a2 61 Double_t min, max, binwidth;
0439b2b7 62 Double_t pmass, lmass, omass, emass, mmass;
8c90f5a2 63 Double_t epsilon, delta, mLL, q, kwHelp, krollWada, formFactor, weight;
64
65 // Get the particle masses
66 // electron
0439b2b7 67 emass = (TDatabasePDG::Instance()->GetParticle(kElectron))->Mass();
68 // muon
69 mmass = (TDatabasePDG::Instance()->GetParticle(kMuonPlus))->Mass();
8c90f5a2 70 // omega
71 pmass = (TDatabasePDG::Instance()->GetParticle(223)) ->Mass();
72 // pi0
73 omass = (TDatabasePDG::Instance()->GetParticle(kPi0)) ->Mass();
74
0439b2b7 75 for ( idecay = 1; idecay<=2; idecay++ )
8c90f5a2 76 {
0439b2b7 77 if ( idecay == 1 )
78 lmass = emass;
79 else
80 lmass = mmass;
81
82 min = 2.0 * lmass;
83 max = pmass - omass;
84 binwidth = (max - min) / (Double_t)nbins;
85 if ( idecay == 1 )
86 fEPMass = new TH1F("fEPMass", "Dalitz electron pair", nbins, min, max);
87 else
88 fMPMass = new TH1F("fMPMass", "Dalitz muon pair", nbins, min, max);
89
90 epsilon = (lmass / pmass) * (lmass / pmass);
91 delta = (omass / pmass) * (omass / pmass);
92
93 for ( ibin = 1; ibin <= nbins; ibin++ )
8c90f5a2 94 {
0439b2b7 95 mLL = min + (Double_t)(ibin - 1) * binwidth + binwidth / 2.0;
96 q = (mLL / pmass) * (mLL / pmass);
97 if ( q <= 4.0 * epsilon )
98 {
8c90f5a2 99 AliFatal("Error in calculating Dalitz mass histogram binning!");
0439b2b7 100 }
101
102 kwHelp = (1.0 + q / (1.0 - delta)) * (1.0 + q / (1.0 - delta))
103 - 4.0 * q / ((1.0 - delta) * (1.0 - delta));
104 if ( kwHelp <= 0.0 )
105 {
8c90f5a2 106 AliFatal("Error in calculating Dalitz mass histogram binning!");
0439b2b7 107 }
108 krollWada = (2.0 / mLL) * TMath::Exp(1.5 * TMath::Log(kwHelp))
109 * TMath::Sqrt(1.0 - 4.0 * epsilon / q)
110 * (1.0 + 2.0 * epsilon / q);
111 formFactor =
8c90f5a2 112 (TMath::Power(TMath::Power(0.6519,2),2))
113 / (TMath::Power(TMath::Power(0.6519,2)-TMath::Power(mLL, 2), 2)
114 + TMath::Power(0.04198, 2)*TMath::Power(0.6519, 2));
0439b2b7 115 weight = krollWada * formFactor;
116 if ( idecay == 1 )
117 fEPMass->AddBinContent(ibin, weight);
118 else
119 fMPMass->AddBinContent(ibin, weight);
120 }
8c90f5a2 121 }
122}
123
124
0439b2b7 125void AliOmegaDalitz::Decay(Int_t idlepton, TLorentzVector* pparent)
8c90f5a2 126{
127//-----------------------------------------------------------------------------
128//
129// Generate Omega Dalitz decay
130//
131//-----------------------------------------------------------------------------
132
133 Double_t pmass, lmass, omass, lpmass;
134 Double_t e1, p1, e3, p3;
135 Double_t betaSquare, lambda;
136 Double_t costheta, sintheta, cosphi, sinphi, phi;
137
138 // Get the particle masses
0439b2b7 139 // lepton
140 lmass = (TDatabasePDG::Instance()->GetParticle(idlepton))->Mass();
8c90f5a2 141 // omega
d060703c 142 pmass = pparent->M();
8c90f5a2 143 // pi0
144 omass = (TDatabasePDG::Instance()->GetParticle(kPi0)) ->Mass();
145
146 // Sample the lepton pair mass from a histogram
147 for( ;; )
148 {
0439b2b7 149 if ( idlepton == kElectron )
150 lpmass = fEPMass->GetRandom();
151 else
152 lpmass = fMPMass->GetRandom();
153 if ( pmass - omass > lpmass && lpmass / 2. > lmass ) break;
8c90f5a2 154 }
155
156 // lepton pair kinematics in virtual photon rest frame
157 e1 = lpmass / 2.;
158 p1 = TMath::Sqrt((e1 + lmass) * (e1 - lmass));
159 betaSquare = 1.0 - 4.0 * (lmass * lmass) / (lpmass * lpmass);
160 lambda = betaSquare / (2.0 - betaSquare);
161 costheta = (2.0 * gRandom->Rndm()) - 1.;
162 sintheta = TMath::Sqrt((1. + costheta) * (1. - costheta));
163 phi = 2.0 * TMath::ACos(-1.) * gRandom->Rndm();
164 sinphi = TMath::Sin(phi);
165 cosphi = TMath::Cos(phi);
166 // momentum vectors of leptons in virtual photon rest frame
167 Double_t pProd1[3] = {p1 * sintheta * cosphi,
168 p1 * sintheta * sinphi,
169 p1 * costheta};
170 Double_t pProd2[3] = {-1.0 * p1 * sintheta * cosphi,
171 -1.0 * p1 * sintheta * sinphi,
172 -1.0 * p1 * costheta};
173
174 // pizero kinematics in omega rest frame
175 e3 = (pmass * pmass + omass * omass - lpmass * lpmass)/(2. * pmass);
176 p3 = TMath::Sqrt((e3 + omass) * (e3 - omass));
177 costheta = (2.0 * gRandom->Rndm()) - 1.;
178 sintheta = TMath::Sqrt((1. + costheta) * (1. - costheta));
179 phi = 2.0 * TMath::ACos(-1.) * gRandom->Rndm();
180 sinphi = TMath::Sin(phi);
181 cosphi = TMath::Cos(phi);
182 // pizero 4-vector in omega rest frame
183 fProducts[2].SetPx(p3 * sintheta * cosphi);
184 fProducts[2].SetPy(p3 * sintheta * sinphi);
185 fProducts[2].SetPz(p3 * costheta);
186 fProducts[2].SetE(e3);
187
188 // lepton 4-vectors in properly rotated virtual photon rest frame
189 Double_t pRot1[3] = {0.};
190 Rot(pProd1, pRot1, costheta, -sintheta, -cosphi, -sinphi);
191 Double_t pRot2[3] = {0.};
192 Rot(pProd2, pRot2, costheta, -sintheta, -cosphi, -sinphi);
193 fProducts[0].SetPx(pRot1[0]);
194 fProducts[0].SetPy(pRot1[1]);
195 fProducts[0].SetPz(pRot1[2]);
196 fProducts[0].SetE(e1);
197 fProducts[1].SetPx(pRot2[0]);
198 fProducts[1].SetPy(pRot2[1]);
199 fProducts[1].SetPz(pRot2[2]);
200 fProducts[1].SetE(e1);
201
202 // boost the dilepton into the omega's rest frame
203 Double_t eLPparent = TMath::Sqrt(p3 * p3 + lpmass * lpmass);
204 TVector3 boostPair( -1.0 * fProducts[2].Px() / eLPparent,
205 -1.0 * fProducts[2].Py() / eLPparent,
206 -1.0 * fProducts[2].Pz() / eLPparent);
207 fProducts[0].Boost(boostPair);
208 fProducts[1].Boost(boostPair);
209
210 // boost all decay products into the lab frame
211 TVector3 boostLab( pparent->Px() / pparent->E(),
212 pparent->Py() / pparent->E(),
213 pparent->Pz() / pparent->E());
214 fProducts[0].Boost(boostLab);
215 fProducts[1].Boost(boostLab);
216 fProducts[2].Boost(boostLab);
217
218 return;
219
220}
221
222Int_t AliOmegaDalitz::ImportParticles(TClonesArray *particles)
223{
224 // Import TParticles in array particles
0439b2b7 225 // l+ l- pi0
8c90f5a2 226
227 TClonesArray &clonesParticles = *particles;
228
0439b2b7 229 Int_t pdg [3] = {kElectron, -kElectron, kPi0};
230 if ( fProducts[1].M() > 0.001 )
231 {
232 pdg[0] = kMuonPlus;
233 pdg[1] = -kMuonPlus;
234 }
235 Int_t parent[3] = {0, 0, -1};
236 Int_t d1 [3] = {-1, -1, 1};
237 Int_t d2 [3] = {-1, -1, 2};
8c90f5a2 238 for (Int_t i = 2; i > -1; i--) {
239 Double_t px = fProducts[i].Px();
240 Double_t py = fProducts[i].Py();
241 Double_t pz = fProducts[i].Pz();
242 Double_t e = fProducts[i].E();
243 //
244 new(clonesParticles[2 - i]) TParticle(pdg[i], 1, parent[i], -1, d1[i], d2[i], px, py, pz, e, 0., 0., 0., 0.);
245 }
246 return (3);
247}
248
249
8c90f5a2 250void AliOmegaDalitz::
251Rot(Double_t pin[3], Double_t pout[3], Double_t costheta, Double_t sintheta,
252 Double_t cosphi, Double_t sinphi)
253{
254 pout[0] = pin[0]*costheta*cosphi-pin[1]*sinphi+pin[2]*sintheta*cosphi;
255 pout[1] = pin[0]*costheta*sinphi+pin[1]*cosphi+pin[2]*sintheta*sinphi;
256 pout[2] = -1.0 * pin[0] * sintheta + pin[2] * costheta;
257 return;
258}
259
05b093f3 260void AliOmegaDalitz::Decay(TClonesArray* array)
261{
262 //
263 // Replace all omega dalitz decays with the correct matrix element decays
264 //
265 printf("-->Correcting Dalitz \n");
266 Int_t nt = array->GetEntriesFast();
267 TParticle* dp[3];
268 for (Int_t i = 0; i < nt; i++) {
269 TParticle* part = (TParticle*) (array->At(i));
270 if (part->GetPdgCode() != 223) continue;
271
272 Int_t fd = part->GetFirstDaughter() - 1;
273 Int_t ld = part->GetLastDaughter() - 1;
274
275 if (fd < 0) continue;
276 if ((ld - fd) != 2) continue;
277
278 for (Int_t j = 0; j < 3; j++) dp[j] = (TParticle*) (array->At(fd+j));
279 if ((dp[0]->GetPdgCode() != kPi0) ||
0439b2b7 280 ((TMath::Abs(dp[1]->GetPdgCode()) != kElectron) &&
281 (TMath::Abs(dp[1]->GetPdgCode()) != kMuonPlus))) continue;
05b093f3 282 TLorentzVector omega(part->Px(), part->Py(), part->Pz(), part->Energy());
0439b2b7 283 if ( TMath::Abs(dp[1]->GetPdgCode()) == kElectron )
284 Decay(kElectron, &omega);
285 else
286 Decay(kMuonPlus, &omega);
05b093f3 287 for (Int_t j = 0; j < 3; j++) dp[j]->SetMomentum(fProducts[2-j]);
288 printf("original %13.3f %13.3f %13.3f %13.3f \n",
289 part->Px(), part->Py(), part->Pz(), part->Energy());
290 printf("new %13.3f %13.3f %13.3f %13.3f \n",
291 dp[0]->Px()+dp[1]->Px()+dp[2]->Px(),
292 dp[0]->Py()+dp[1]->Py()+dp[2]->Py(),
293 dp[0]->Pz()+dp[1]->Pz()+dp[2]->Pz(),
294 dp[0]->Energy()+dp[1]->Energy()+dp[2]->Energy());
295
296
297 }
298}
299AliOmegaDalitz& AliOmegaDalitz::operator=(const AliOmegaDalitz& rhs)
300{
301// Assignment operator
302 rhs.Copy(*this);
303 return *this;
304}
305
306void AliOmegaDalitz::Copy(TObject&) const
307{
308 //
309 // Copy
310 //
311 Fatal("Copy","Not implemented!\n");
312}
313
314AliOmegaDalitz::AliOmegaDalitz(const AliOmegaDalitz &dalitz)
315 : AliDecayer(),
0439b2b7 316 fEPMass(0),
317 fMPMass(0)
05b093f3 318{
319 // Copy constructor
320 dalitz.Copy(*this);
321}