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4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
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14 **************************************************************************/
18 //____________________________________________________________________
20 // Reconstruct charged particle multiplicity in the FMD
22 // [See also the AliFMDReconstructor class]
24 // This class reconstructs the muliplicity in regions based on the
25 // ratio of empty to full strips.
27 #include "AliFMD.h" // ALIFMD_H
28 #include "AliFMDMultPoisson.h" // ALIFMDMULTPOISSON_H
29 #include "AliFMDMultRegion.h" // ALIFMDMULTREGION_H
30 #include "AliFMDDigit.h" // ALIFMDDIGIT_H
31 #include "AliLog.h" // ALILOG_H
32 #include <TClonesArray.h> // ROOT_TClonesArray
33 #include <TTree.h> // ROOT_TTree
35 //____________________________________________________________________
36 ClassImp(AliFMDMultPoisson)
38 //____________________________________________________________________
39 AliFMDMultPoisson::AliFMDMultPoisson()
40 : AliFMDMultAlgorithm("Poisson", "Poisson"),
48 fMult = new TClonesArray("AliFMDMultRegion", 1000);
51 //____________________________________________________________________
53 AliFMDMultPoisson::PreEvent(TTree* tree, Float_t ipZ)
55 // Reset internal data
56 AliFMDMultAlgorithm::PreEvent(tree, ipZ);
57 fCurrentVertexZ = ipZ;
60 // Make a branch in the reconstruction tree.
61 const Int_t kBufferSize = 16000;
62 fTreeR->Branch("FMDPoisson", &fMult, kBufferSize);
66 //____________________________________________________________________
68 AliFMDMultPoisson::ProcessDigit(AliFMDDigit* digit,
77 // digit Digit to process
78 // ipZ Z--coordinate of the primary interaction
79 // vertex of this event
82 if (count < fThreshold) fEmpty(digit->Detector() - 1,
85 digit->Strip()) = kTRUE;
88 //____________________________________________________________________
90 AliFMDMultPoisson::PostEvent()
93 // Based on the information in the cache, do the reconstruction.
95 // Loop over the detectors
96 for (Int_t i = 1; i <= 3; i++) {
97 AliFMDSubDetector* sub = 0;
99 case 1: sub = fFMD->GetFMD1(); break;
100 case 2: sub = fFMD->GetFMD2(); break;
101 case 3: sub = fFMD->GetFMD3(); break;
105 // Loop over the rings in the detector
106 for (Int_t j = 0; j < 2; j++) {
110 case 0: r = sub->GetInner(); rZ = sub->GetInnerZ(); break;
111 case 1: r = sub->GetOuter(); rZ = sub->GetOuterZ(); break;
115 // Calculate low/high theta and eta
116 // FIXME: Is this right?
117 Float_t realZ = fCurrentVertexZ + rZ;
118 Float_t thetaOut = TMath::ATan2(r->GetHighR(), realZ);
119 Float_t thetaIn = TMath::ATan2(r->GetLowR(), realZ);
120 Float_t etaOut = - TMath::Log(TMath::Tan(thetaOut / 2));
121 Float_t etaIn = - TMath::Log(TMath::Tan(thetaIn / 2));
122 if (TMath::Abs(etaOut) > TMath::Abs(etaIn)) {
128 //-------------------------------------------------------------
130 // Here starts poisson method
132 // Calculate eta step per strip, number of eta steps, number of
133 // phi steps, and check the sign of the eta increment
134 Float_t stripEta = (Float_t(r->GetNStrips()) / (etaIn - etaOut));
135 Int_t nEta = Int_t(TMath::Abs(etaIn - etaOut) / fDeltaEta);
136 Int_t nPhi = Int_t(360. / fDeltaPhi);
137 Float_t sign = TMath::Sign(Float_t(1.), etaIn);
139 AliDebug(10, Form("FMD%d%c Eta range: %f, %f %d Phi steps",
140 sub->GetId(), r->GetId(), etaOut, etaIn, nPhi));
142 // Loop over relevant phi values
143 for (Int_t p = 0; p < nPhi; p++) {
144 Float_t minPhi = p * fDeltaPhi;
145 Float_t maxPhi = minPhi + fDeltaPhi;
146 UShort_t minSector = UShort_t(minPhi / 360) * r->GetNSectors();
147 UShort_t maxSector = UShort_t(maxPhi / 360) * r->GetNSectors();
149 AliDebug(10, Form(" Now in phi range %f, %f (sectors %d,%d)",
150 minPhi, maxPhi, minSector, maxSector));
151 // Loop over relevant eta values
152 for (Int_t e = nEta; e >= 0; --e) {
153 Float_t maxEta = etaIn - sign * e * fDeltaEta;
154 Float_t minEta = maxEta - sign * fDeltaEta;
155 if (sign > 0) minEta = TMath::Max(minEta, etaOut);
156 else minEta = TMath::Min(minEta, etaOut);
157 Float_t theta1 = 2 * TMath::ATan(TMath::Exp(-minEta));
158 Float_t theta2 = 2 * TMath::ATan(TMath::Exp(-maxEta));
159 Float_t minR = TMath::Abs(realZ * TMath::Tan(theta2));
160 Float_t maxR = TMath::Abs(realZ * TMath::Tan(theta1));
161 UShort_t minStrip = UShort_t((etaIn - maxEta) * stripEta + 0.5);
162 UShort_t maxStrip = UShort_t((etaIn - minEta) * stripEta + 0.5);
164 AliDebug(10, Form(" Now in eta range %f, %f (strips %d, %d)\n"
165 " [radii %f, %f, thetas %f, %f, sign %d]",
166 minEta, maxEta, minStrip, maxStrip,
167 minR, maxR, theta1, theta2, sign));
169 // Count number of empty strips
170 Int_t emptyStrips = 0;
171 for (Int_t sector = minSector; sector < maxSector; sector++)
172 for (Int_t strip = minStrip; strip < maxStrip; strip++)
173 if (fEmpty(sub->GetId() - 1, r->GetId(), sector, strip))
176 // The total number of strips
177 Float_t nTotal = (maxSector - minSector) * (maxStrip - minStrip);
179 // Log ratio of empty to total number of strips
180 AliDebug(10, Form("Lambda= %d / %d = %f",
182 Float_t(emptyStrips) / nTotal));
184 Double_t lambda = (emptyStrips > 0 ?
185 - TMath::Log(Double_t(emptyStrips) / nTotal) :
188 // The reconstructed number of particles is then given by
189 Int_t reconstructed = Int_t(lambda * nTotal + 0.5);
191 // Add a AliFMDMultRegion to the reconstruction tree.
192 AliFMDMultRegion* m = new((*fMult)[fNMult])
193 AliFMDMultRegion(sub->GetId(), r->GetId(),
194 minSector, maxSector, minStrip, maxStrip,
195 minEta, maxEta, minPhi, maxPhi,
196 reconstructed, AliFMDMultRegion::kPoission);
206 //____________________________________________________________________