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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 | ||
31 | ClassImp(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 | // | |
49 | AliOmegaDalitz::AliOmegaDalitz(): | |
50 | AliDecayer(), | |
0439b2b7 | 51 | fEPMass(0), |
b8f95537 | 52 | fMPMass(0), |
53 | fInit(0) | |
8c90f5a2 | 54 | { |
55 | // Constructor | |
56 | } | |
57 | ||
58 | void AliOmegaDalitz::Init() | |
59 | { | |
60 | // Initialisation | |
0439b2b7 | 61 | Int_t idecay, ibin, nbins = 1000; |
8c90f5a2 | 62 | Double_t min, max, binwidth; |
0439b2b7 | 63 | Double_t pmass, lmass, omass, emass, mmass; |
8c90f5a2 | 64 | Double_t epsilon, delta, mLL, q, kwHelp, krollWada, formFactor, weight; |
65 | ||
66 | // Get the particle masses | |
67 | // electron | |
0439b2b7 | 68 | emass = (TDatabasePDG::Instance()->GetParticle(kElectron))->Mass(); |
69 | // muon | |
70 | mmass = (TDatabasePDG::Instance()->GetParticle(kMuonPlus))->Mass(); | |
8c90f5a2 | 71 | // omega |
72 | pmass = (TDatabasePDG::Instance()->GetParticle(223)) ->Mass(); | |
73 | // pi0 | |
74 | omass = (TDatabasePDG::Instance()->GetParticle(kPi0)) ->Mass(); | |
75 | ||
0439b2b7 | 76 | for ( idecay = 1; idecay<=2; idecay++ ) |
8c90f5a2 | 77 | { |
0439b2b7 | 78 | if ( idecay == 1 ) |
79 | lmass = emass; | |
80 | else | |
81 | lmass = mmass; | |
82 | ||
83 | min = 2.0 * lmass; | |
84 | max = pmass - omass; | |
85 | binwidth = (max - min) / (Double_t)nbins; | |
86 | if ( idecay == 1 ) | |
87 | fEPMass = new TH1F("fEPMass", "Dalitz electron pair", nbins, min, max); | |
88 | else | |
89 | fMPMass = new TH1F("fMPMass", "Dalitz muon pair", nbins, min, max); | |
90 | ||
91 | epsilon = (lmass / pmass) * (lmass / pmass); | |
92 | delta = (omass / pmass) * (omass / pmass); | |
93 | ||
94 | for ( ibin = 1; ibin <= nbins; ibin++ ) | |
8c90f5a2 | 95 | { |
0439b2b7 | 96 | mLL = min + (Double_t)(ibin - 1) * binwidth + binwidth / 2.0; |
97 | q = (mLL / pmass) * (mLL / pmass); | |
98 | if ( q <= 4.0 * epsilon ) | |
99 | { | |
8c90f5a2 | 100 | AliFatal("Error in calculating Dalitz mass histogram binning!"); |
0439b2b7 | 101 | } |
102 | ||
103 | kwHelp = (1.0 + q / (1.0 - delta)) * (1.0 + q / (1.0 - delta)) | |
104 | - 4.0 * q / ((1.0 - delta) * (1.0 - delta)); | |
105 | if ( kwHelp <= 0.0 ) | |
106 | { | |
8c90f5a2 | 107 | AliFatal("Error in calculating Dalitz mass histogram binning!"); |
0439b2b7 | 108 | } |
109 | krollWada = (2.0 / mLL) * TMath::Exp(1.5 * TMath::Log(kwHelp)) | |
110 | * TMath::Sqrt(1.0 - 4.0 * epsilon / q) | |
111 | * (1.0 + 2.0 * epsilon / q); | |
112 | formFactor = | |
8c90f5a2 | 113 | (TMath::Power(TMath::Power(0.6519,2),2)) |
114 | / (TMath::Power(TMath::Power(0.6519,2)-TMath::Power(mLL, 2), 2) | |
115 | + TMath::Power(0.04198, 2)*TMath::Power(0.6519, 2)); | |
0439b2b7 | 116 | weight = krollWada * formFactor; |
117 | if ( idecay == 1 ) | |
118 | fEPMass->AddBinContent(ibin, weight); | |
119 | else | |
120 | fMPMass->AddBinContent(ibin, weight); | |
121 | } | |
8c90f5a2 | 122 | } |
123 | } | |
124 | ||
125 | ||
cc1f7ac3 | 126 | void AliOmegaDalitz::Decay(Int_t idlepton, TLorentzVector* pparent) |
8c90f5a2 | 127 | { |
128 | //----------------------------------------------------------------------------- | |
129 | // | |
130 | // Generate Omega Dalitz decay | |
131 | // | |
132 | //----------------------------------------------------------------------------- | |
133 | ||
b8f95537 | 134 | if (!fInit) { |
135 | Init(); | |
136 | fInit=1; | |
137 | } | |
138 | ||
8c90f5a2 | 139 | Double_t pmass, lmass, omass, lpmass; |
140 | Double_t e1, p1, e3, p3; | |
141 | Double_t betaSquare, lambda; | |
142 | Double_t costheta, sintheta, cosphi, sinphi, phi; | |
143 | ||
144 | // Get the particle masses | |
0439b2b7 | 145 | // lepton |
146 | lmass = (TDatabasePDG::Instance()->GetParticle(idlepton))->Mass(); | |
8c90f5a2 | 147 | // omega |
d060703c | 148 | pmass = pparent->M(); |
8c90f5a2 | 149 | // pi0 |
150 | omass = (TDatabasePDG::Instance()->GetParticle(kPi0)) ->Mass(); | |
151 | ||
152 | // Sample the lepton pair mass from a histogram | |
153 | for( ;; ) | |
154 | { | |
0439b2b7 | 155 | if ( idlepton == kElectron ) |
156 | lpmass = fEPMass->GetRandom(); | |
157 | else | |
158 | lpmass = fMPMass->GetRandom(); | |
159 | if ( pmass - omass > lpmass && lpmass / 2. > lmass ) break; | |
8c90f5a2 | 160 | } |
161 | ||
162 | // lepton pair kinematics in virtual photon rest frame | |
163 | e1 = lpmass / 2.; | |
164 | p1 = TMath::Sqrt((e1 + lmass) * (e1 - lmass)); | |
165 | betaSquare = 1.0 - 4.0 * (lmass * lmass) / (lpmass * lpmass); | |
166 | lambda = betaSquare / (2.0 - betaSquare); | |
167 | costheta = (2.0 * gRandom->Rndm()) - 1.; | |
168 | sintheta = TMath::Sqrt((1. + costheta) * (1. - costheta)); | |
169 | phi = 2.0 * TMath::ACos(-1.) * gRandom->Rndm(); | |
170 | sinphi = TMath::Sin(phi); | |
171 | cosphi = TMath::Cos(phi); | |
172 | // momentum vectors of leptons in virtual photon rest frame | |
173 | Double_t pProd1[3] = {p1 * sintheta * cosphi, | |
174 | p1 * sintheta * sinphi, | |
175 | p1 * costheta}; | |
176 | Double_t pProd2[3] = {-1.0 * p1 * sintheta * cosphi, | |
177 | -1.0 * p1 * sintheta * sinphi, | |
178 | -1.0 * p1 * costheta}; | |
179 | ||
180 | // pizero kinematics in omega rest frame | |
181 | e3 = (pmass * pmass + omass * omass - lpmass * lpmass)/(2. * pmass); | |
182 | p3 = TMath::Sqrt((e3 + omass) * (e3 - omass)); | |
183 | costheta = (2.0 * gRandom->Rndm()) - 1.; | |
184 | sintheta = TMath::Sqrt((1. + costheta) * (1. - costheta)); | |
185 | phi = 2.0 * TMath::ACos(-1.) * gRandom->Rndm(); | |
186 | sinphi = TMath::Sin(phi); | |
187 | cosphi = TMath::Cos(phi); | |
188 | // pizero 4-vector in omega rest frame | |
189 | fProducts[2].SetPx(p3 * sintheta * cosphi); | |
190 | fProducts[2].SetPy(p3 * sintheta * sinphi); | |
191 | fProducts[2].SetPz(p3 * costheta); | |
192 | fProducts[2].SetE(e3); | |
193 | ||
194 | // lepton 4-vectors in properly rotated virtual photon rest frame | |
195 | Double_t pRot1[3] = {0.}; | |
196 | Rot(pProd1, pRot1, costheta, -sintheta, -cosphi, -sinphi); | |
197 | Double_t pRot2[3] = {0.}; | |
198 | Rot(pProd2, pRot2, costheta, -sintheta, -cosphi, -sinphi); | |
199 | fProducts[0].SetPx(pRot1[0]); | |
200 | fProducts[0].SetPy(pRot1[1]); | |
201 | fProducts[0].SetPz(pRot1[2]); | |
202 | fProducts[0].SetE(e1); | |
203 | fProducts[1].SetPx(pRot2[0]); | |
204 | fProducts[1].SetPy(pRot2[1]); | |
205 | fProducts[1].SetPz(pRot2[2]); | |
206 | fProducts[1].SetE(e1); | |
207 | ||
208 | // boost the dilepton into the omega's rest frame | |
209 | Double_t eLPparent = TMath::Sqrt(p3 * p3 + lpmass * lpmass); | |
210 | TVector3 boostPair( -1.0 * fProducts[2].Px() / eLPparent, | |
211 | -1.0 * fProducts[2].Py() / eLPparent, | |
212 | -1.0 * fProducts[2].Pz() / eLPparent); | |
213 | fProducts[0].Boost(boostPair); | |
214 | fProducts[1].Boost(boostPair); | |
215 | ||
216 | // boost all decay products into the lab frame | |
217 | TVector3 boostLab( pparent->Px() / pparent->E(), | |
218 | pparent->Py() / pparent->E(), | |
219 | pparent->Pz() / pparent->E()); | |
220 | fProducts[0].Boost(boostLab); | |
221 | fProducts[1].Boost(boostLab); | |
222 | fProducts[2].Boost(boostLab); | |
223 | ||
224 | return; | |
225 | ||
226 | } | |
227 | ||
228 | Int_t AliOmegaDalitz::ImportParticles(TClonesArray *particles) | |
229 | { | |
230 | // Import TParticles in array particles | |
0439b2b7 | 231 | // l+ l- pi0 |
8c90f5a2 | 232 | |
233 | TClonesArray &clonesParticles = *particles; | |
234 | ||
0439b2b7 | 235 | Int_t pdg [3] = {kElectron, -kElectron, kPi0}; |
236 | if ( fProducts[1].M() > 0.001 ) | |
237 | { | |
238 | pdg[0] = kMuonPlus; | |
239 | pdg[1] = -kMuonPlus; | |
240 | } | |
241 | Int_t parent[3] = {0, 0, -1}; | |
242 | Int_t d1 [3] = {-1, -1, 1}; | |
243 | Int_t d2 [3] = {-1, -1, 2}; | |
8c90f5a2 | 244 | for (Int_t i = 2; i > -1; i--) { |
245 | Double_t px = fProducts[i].Px(); | |
246 | Double_t py = fProducts[i].Py(); | |
247 | Double_t pz = fProducts[i].Pz(); | |
248 | Double_t e = fProducts[i].E(); | |
249 | // | |
250 | new(clonesParticles[2 - i]) TParticle(pdg[i], 1, parent[i], -1, d1[i], d2[i], px, py, pz, e, 0., 0., 0., 0.); | |
251 | } | |
252 | return (3); | |
253 | } | |
254 | ||
255 | ||
8c90f5a2 | 256 | void AliOmegaDalitz:: |
257 | Rot(Double_t pin[3], Double_t pout[3], Double_t costheta, Double_t sintheta, | |
271e6aae | 258 | Double_t cosphi, Double_t sinphi) const |
8c90f5a2 | 259 | { |
43ce81af | 260 | // Perform rotation |
8c90f5a2 | 261 | pout[0] = pin[0]*costheta*cosphi-pin[1]*sinphi+pin[2]*sintheta*cosphi; |
262 | pout[1] = pin[0]*costheta*sinphi+pin[1]*cosphi+pin[2]*sintheta*sinphi; | |
263 | pout[2] = -1.0 * pin[0] * sintheta + pin[2] * costheta; | |
264 | return; | |
265 | } | |
266 | ||
05b093f3 | 267 | void AliOmegaDalitz::Decay(TClonesArray* array) |
268 | { | |
269 | // | |
270 | // Replace all omega dalitz decays with the correct matrix element decays | |
271 | // | |
272 | printf("-->Correcting Dalitz \n"); | |
273 | Int_t nt = array->GetEntriesFast(); | |
274 | TParticle* dp[3]; | |
275 | for (Int_t i = 0; i < nt; i++) { | |
276 | TParticle* part = (TParticle*) (array->At(i)); | |
277 | if (part->GetPdgCode() != 223) continue; | |
278 | ||
279 | Int_t fd = part->GetFirstDaughter() - 1; | |
280 | Int_t ld = part->GetLastDaughter() - 1; | |
281 | ||
282 | if (fd < 0) continue; | |
283 | if ((ld - fd) != 2) continue; | |
284 | ||
285 | for (Int_t j = 0; j < 3; j++) dp[j] = (TParticle*) (array->At(fd+j)); | |
286 | if ((dp[0]->GetPdgCode() != kPi0) || | |
0439b2b7 | 287 | ((TMath::Abs(dp[1]->GetPdgCode()) != kElectron) && |
288 | (TMath::Abs(dp[1]->GetPdgCode()) != kMuonPlus))) continue; | |
05b093f3 | 289 | TLorentzVector omega(part->Px(), part->Py(), part->Pz(), part->Energy()); |
0439b2b7 | 290 | if ( TMath::Abs(dp[1]->GetPdgCode()) == kElectron ) |
291 | Decay(kElectron, &omega); | |
292 | else | |
293 | Decay(kMuonPlus, &omega); | |
05b093f3 | 294 | for (Int_t j = 0; j < 3; j++) dp[j]->SetMomentum(fProducts[2-j]); |
295 | printf("original %13.3f %13.3f %13.3f %13.3f \n", | |
296 | part->Px(), part->Py(), part->Pz(), part->Energy()); | |
297 | printf("new %13.3f %13.3f %13.3f %13.3f \n", | |
298 | dp[0]->Px()+dp[1]->Px()+dp[2]->Px(), | |
299 | dp[0]->Py()+dp[1]->Py()+dp[2]->Py(), | |
300 | dp[0]->Pz()+dp[1]->Pz()+dp[2]->Pz(), | |
301 | dp[0]->Energy()+dp[1]->Energy()+dp[2]->Energy()); | |
302 | ||
303 | ||
304 | } | |
305 | } | |
306 | AliOmegaDalitz& AliOmegaDalitz::operator=(const AliOmegaDalitz& rhs) | |
307 | { | |
308 | // Assignment operator | |
309 | rhs.Copy(*this); | |
310 | return *this; | |
311 | } | |
312 | ||
313 | void AliOmegaDalitz::Copy(TObject&) const | |
314 | { | |
315 | // | |
316 | // Copy | |
317 | // | |
318 | Fatal("Copy","Not implemented!\n"); | |
319 | } | |
320 | ||
321 | AliOmegaDalitz::AliOmegaDalitz(const AliOmegaDalitz &dalitz) | |
322 | : AliDecayer(), | |
0439b2b7 | 323 | fEPMass(0), |
b8f95537 | 324 | fMPMass(0), |
325 | fInit(0) | |
05b093f3 | 326 | { |
327 | // Copy constructor | |
328 | dalitz.Copy(*this); | |
329 | } |