1 /**************************************************************************
2 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
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 **************************************************************************/
18 ///////////////////////////////////////////////////////////////////////////////
20 // particle id probability densities //
22 // The AliPID class stores the probability densities for the different //
23 // particle type hypotheses electron, muon, pion, kaon, proton, photon, //
24 // pi0, neutron, K0 and electron conversion. These probability densities //
25 // are determined from the detector response functions. //
26 // The * and *= operators are overloaded for AliPID to combine the PIDs //
27 // from different detectors. //
29 // The Bayesian probability to be a particle of a given type can be //
30 // calculated from the probability densities, if the a priori probabilities //
31 // (or abundences, concentrations) of particle species are known. These //
32 // priors can be given as argument to the GetProbability or GetMostProbable //
33 // method or they can be set globally by calling the static method //
36 // The implementation of this class is based on the note ... //
37 // by Iouri Belikov and Karel Safarik. //
39 ///////////////////////////////////////////////////////////////////////////////
42 #include <TDatabasePDG.h>
48 #define M(PID) TDatabasePDG::Instance()->GetParticle(fgkParticleCode[(PID)])->Mass()
52 const char* AliPID::fgkParticleName[AliPID::kSPECIESN+1] = {
66 const Int_t AliPID::fgkParticleCode[AliPID::kSPECIESN+1] = {
80 /*const*/ Float_t AliPID::fgkParticleMass[AliPID::kSPECIESN+1] = {
81 0,0,0,0,0,0,0,0,0,0,0
83 M(kElectron), // electron
90 M(kNeutron), // neutron
92 M(kEleCon), // electron conversion
97 Double_t AliPID::fgPrior[kSPECIESN] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
100 //_______________________________________________________________________
106 // Default constructor
109 // set default values (= equal probabilities)
110 for (Int_t i = 0; i < kSPECIESN; i++)
111 fProbDensity[i] = 1./kSPECIESN;
114 //_______________________________________________________________________
115 AliPID::AliPID(const Double_t* probDensity, Bool_t charged) :
120 // Standard constructor
123 // set given probability densities
124 for (Int_t i = 0; i < kSPECIES; i++)
125 fProbDensity[i] = probDensity[i];
127 for (Int_t i = kSPECIES; i < kSPECIESN; i++)
128 fProbDensity[i] = ((charged) ? 0 : probDensity[i]);
131 //_______________________________________________________________________
132 AliPID::AliPID(const Float_t* probDensity, Bool_t charged) :
137 // Standard constructor
140 // set given probability densities
141 for (Int_t i = 0; i < kSPECIES; i++)
142 fProbDensity[i] = probDensity[i];
144 for (Int_t i = kSPECIES; i < kSPECIESN; i++)
145 fProbDensity[i] = ((charged) ? 0 : probDensity[i]);
148 //_______________________________________________________________________
149 AliPID::AliPID(const AliPID& pid) :
151 fCharged(pid.fCharged)
156 // We do not call init here, MUST already be done
157 for (Int_t i = 0; i < kSPECIESN; i++)
158 fProbDensity[i] = pid.fProbDensity[i];
161 //_______________________________________________________________________
162 AliPID& AliPID::operator = (const AliPID& pid)
164 // assignment operator
166 fCharged = pid.fCharged;
167 for (Int_t i = 0; i < kSPECIESN; i++) {
168 fProbDensity[i] = pid.fProbDensity[i];
173 //_______________________________________________________________________
177 // Initialise the masses
179 // Initialise only once...
180 if(!fgkParticleMass[0])
181 for (Int_t i = 0; i < kSPECIESN; i++)
182 fgkParticleMass[i] = M(i);
185 //_____________________________________________________________________________
186 Double_t AliPID::GetProbability(EParticleType iType,
187 const Double_t* prior) const
190 // Get the probability to be a particle of type "iType"
191 // assuming the a priori probabilities "prior"
194 Int_t nSpecies = ((fCharged) ? kSPECIES : kSPECIESN);
195 for (Int_t i = 0; i < nSpecies; i++) {
196 sum += fProbDensity[i] * prior[i];
199 AliError("Invalid probability densities or priors");
202 return fProbDensity[iType] * prior[iType] / sum;
205 //_____________________________________________________________________________
206 Double_t AliPID::GetProbability(EParticleType iType) const
208 // get the probability to be a particle of type "iType"
209 // assuming the globaly set a priori probabilities
211 return GetProbability(iType, fgPrior);
214 //_____________________________________________________________________________
215 void AliPID::GetProbabilities(Double_t* probabilities,
216 const Double_t* prior) const
218 // get the probabilities to be a particle of given type
219 // assuming the a priori probabilities "prior"
222 Int_t nSpecies = ((fCharged) ? kSPECIES : kSPECIESN);
223 for (Int_t i = 0; i < nSpecies; i++) {
224 sum += fProbDensity[i] * prior[i];
227 AliError("Invalid probability densities or priors");
228 for (Int_t i = 0; i < nSpecies; i++) probabilities[i] = -1;
231 for (Int_t i = 0; i < nSpecies; i++) {
232 probabilities[i] = fProbDensity[i] * prior[i] / sum;
236 //_____________________________________________________________________________
237 void AliPID::GetProbabilities(Double_t* probabilities) const
239 // get the probabilities to be a particle of given type
240 // assuming the globaly set a priori probabilities
242 GetProbabilities(probabilities, fgPrior);
245 //_____________________________________________________________________________
246 AliPID::EParticleType AliPID::GetMostProbable(const Double_t* prior) const
248 // get the most probable particle id hypothesis
249 // assuming the a priori probabilities "prior"
252 EParticleType id = kPion;
253 Int_t nSpecies = ((fCharged) ? kSPECIES : kSPECIESN);
254 for (Int_t i = 0; i < nSpecies; i++) {
255 Double_t prob = fProbDensity[i] * prior[i];
258 id = EParticleType(i);
262 AliError("Invalid probability densities or priors");
267 //_____________________________________________________________________________
268 AliPID::EParticleType AliPID::GetMostProbable() const
270 // get the most probable particle id hypothesis
271 // assuming the globaly set a priori probabilities
273 return GetMostProbable(fgPrior);
277 //_____________________________________________________________________________
278 void AliPID::SetPriors(const Double_t* prior, Bool_t charged)
280 // use the given priors as global a priori probabilities
283 for (Int_t i = 0; i < kSPECIESN; i++) {
284 if (charged && (i >= kSPECIES)) {
288 AliWarningClass(Form("negative prior (%g) for %ss. "
289 "Using 0 instead.", prior[i],
290 fgkParticleName[i]));
293 fgPrior[i] = prior[i];
299 AliWarningClass("all priors are zero.");
303 //_____________________________________________________________________________
304 void AliPID::SetPrior(EParticleType iType, Double_t prior)
306 // use the given prior as global a priori probability for particles
310 AliWarningClass(Form("negative prior (%g) for %ss. Using 0 instead.",
311 prior, fgkParticleName[iType]));
314 fgPrior[iType] = prior;
318 //_____________________________________________________________________________
319 AliPID& AliPID::operator *= (const AliPID& pid)
321 // combine this probability densities with the one of "pid"
323 for (Int_t i = 0; i < kSPECIESN; i++) {
324 fProbDensity[i] *= pid.fProbDensity[i];
329 //_____________________________________________________________________________
330 AliPID operator * (const AliPID& pid1, const AliPID& pid2)
332 // combine the two probability densities