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 char* AliPID::fgkParticleShortName[AliPID::kSPECIESN+1] = {
80 const char* AliPID::fgkParticleLatexName[AliPID::kSPECIESN+1] = {
94 const Int_t AliPID::fgkParticleCode[AliPID::kSPECIESN+1] = {
108 /*const*/ Float_t AliPID::fgkParticleMass[AliPID::kSPECIESN+1] = {
109 0,0,0,0,0,0,0,0,0,0,0
111 M(kElectron), // electron
115 M(kProton), // proton
116 M(kPhoton), // photon
118 M(kNeutron), // neutron
120 M(kEleCon), // electron conversion
125 Double_t AliPID::fgPrior[kSPECIESN] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
128 //_______________________________________________________________________
134 // Default constructor
137 // set default values (= equal probabilities)
138 for (Int_t i = 0; i < kSPECIESN; i++)
139 fProbDensity[i] = 1./kSPECIESN;
142 //_______________________________________________________________________
143 AliPID::AliPID(const Double_t* probDensity, Bool_t charged) :
148 // Standard constructor
151 // set given probability densities
152 for (Int_t i = 0; i < kSPECIES; i++)
153 fProbDensity[i] = probDensity[i];
155 for (Int_t i = kSPECIES; i < kSPECIESN; i++)
156 fProbDensity[i] = ((charged) ? 0 : probDensity[i]);
159 //_______________________________________________________________________
160 AliPID::AliPID(const Float_t* probDensity, Bool_t charged) :
165 // Standard constructor
168 // set given probability densities
169 for (Int_t i = 0; i < kSPECIES; i++)
170 fProbDensity[i] = probDensity[i];
172 for (Int_t i = kSPECIES; i < kSPECIESN; i++)
173 fProbDensity[i] = ((charged) ? 0 : probDensity[i]);
176 //_______________________________________________________________________
177 AliPID::AliPID(const AliPID& pid) :
179 fCharged(pid.fCharged)
184 // We do not call init here, MUST already be done
185 for (Int_t i = 0; i < kSPECIESN; i++)
186 fProbDensity[i] = pid.fProbDensity[i];
189 //_______________________________________________________________________
190 void AliPID::SetProbabilities(const Double_t* probDensity, Bool_t charged)
193 // Set the probability densities
195 for (Int_t i = 0; i < kSPECIES; i++)
196 fProbDensity[i] = probDensity[i];
198 for (Int_t i = kSPECIES; i < kSPECIESN; i++)
199 fProbDensity[i] = ((charged) ? 0 : probDensity[i]);
202 //_______________________________________________________________________
203 AliPID& AliPID::operator = (const AliPID& pid)
205 // assignment operator
207 fCharged = pid.fCharged;
208 for (Int_t i = 0; i < kSPECIESN; i++) {
209 fProbDensity[i] = pid.fProbDensity[i];
214 //_______________________________________________________________________
218 // Initialise the masses
220 // Initialise only once...
221 if(!fgkParticleMass[0])
222 for (Int_t i = 0; i < kSPECIESN; i++)
223 fgkParticleMass[i] = M(i);
226 //_____________________________________________________________________________
227 Double_t AliPID::GetProbability(EParticleType iType,
228 const Double_t* prior) const
231 // Get the probability to be a particle of type "iType"
232 // assuming the a priori probabilities "prior"
235 Int_t nSpecies = ((fCharged) ? kSPECIES : kSPECIESN);
236 for (Int_t i = 0; i < nSpecies; i++) {
237 sum += fProbDensity[i] * prior[i];
240 AliError("Invalid probability densities or priors");
243 return fProbDensity[iType] * prior[iType] / sum;
246 //_____________________________________________________________________________
247 Double_t AliPID::GetProbability(EParticleType iType) const
249 // get the probability to be a particle of type "iType"
250 // assuming the globaly set a priori probabilities
252 return GetProbability(iType, fgPrior);
255 //_____________________________________________________________________________
256 void AliPID::GetProbabilities(Double_t* probabilities,
257 const Double_t* prior) const
259 // get the probabilities to be a particle of given type
260 // assuming the a priori probabilities "prior"
263 Int_t nSpecies = ((fCharged) ? kSPECIES : kSPECIESN);
264 for (Int_t i = 0; i < nSpecies; i++) {
265 sum += fProbDensity[i] * prior[i];
268 AliError("Invalid probability densities or priors");
269 for (Int_t i = 0; i < nSpecies; i++) probabilities[i] = -1;
272 for (Int_t i = 0; i < nSpecies; i++) {
273 probabilities[i] = fProbDensity[i] * prior[i] / sum;
277 //_____________________________________________________________________________
278 void AliPID::GetProbabilities(Double_t* probabilities) const
280 // get the probabilities to be a particle of given type
281 // assuming the globaly set a priori probabilities
283 GetProbabilities(probabilities, fgPrior);
286 //_____________________________________________________________________________
287 AliPID::EParticleType AliPID::GetMostProbable(const Double_t* prior) const
289 // get the most probable particle id hypothesis
290 // assuming the a priori probabilities "prior"
293 EParticleType id = kPion;
294 Int_t nSpecies = ((fCharged) ? kSPECIES : kSPECIESN);
295 for (Int_t i = 0; i < nSpecies; i++) {
296 Double_t prob = fProbDensity[i] * prior[i];
299 id = EParticleType(i);
303 AliError("Invalid probability densities or priors");
308 //_____________________________________________________________________________
309 AliPID::EParticleType AliPID::GetMostProbable() const
311 // get the most probable particle id hypothesis
312 // assuming the globaly set a priori probabilities
314 return GetMostProbable(fgPrior);
318 //_____________________________________________________________________________
319 void AliPID::SetPriors(const Double_t* prior, Bool_t charged)
321 // use the given priors as global a priori probabilities
324 for (Int_t i = 0; i < kSPECIESN; i++) {
325 if (charged && (i >= kSPECIES)) {
329 AliWarningClass(Form("negative prior (%g) for %ss. "
330 "Using 0 instead.", prior[i],
331 fgkParticleName[i]));
334 fgPrior[i] = prior[i];
340 AliWarningClass("all priors are zero.");
344 //_____________________________________________________________________________
345 void AliPID::SetPrior(EParticleType iType, Double_t prior)
347 // use the given prior as global a priori probability for particles
351 AliWarningClass(Form("negative prior (%g) for %ss. Using 0 instead.",
352 prior, fgkParticleName[iType]));
355 fgPrior[iType] = prior;
359 //_____________________________________________________________________________
360 AliPID& AliPID::operator *= (const AliPID& pid)
362 // combine this probability densities with the one of "pid"
364 for (Int_t i = 0; i < kSPECIESN; i++) {
365 fProbDensity[i] *= pid.fProbDensity[i];
370 //_____________________________________________________________________________
371 AliPID operator * (const AliPID& pid1, const AliPID& pid2)
373 // combine the two probability densities