1 //---------------------------------------------------------------------------------
2 // The AliKFParticleBase class
4 // @author S.Gorbunov, I.Kisel
8 // Class to reconstruct and store the decayed particle parameters.
9 // The method is described in CBM-SOFT note 2007-003,
10 // ``Reconstruction of decayed particles based on the Kalman filter'',
11 // http://www.gsi.de/documents/DOC-2007-May-14-1.pdf
13 // This class describes general mathematics which is used by AliKFParticle class
15 // -= Copyright © ALICE HLT Group =-
16 //_________________________________________________________________________________
20 #ifndef ALIKFPARTICLEBASE_H
21 #define ALIKFPARTICLEBASE_H
25 class AliKFParticleBase :public TObject {
30 //* ABSTRACT METHODS HAVE TO BE DEFINED IN USER CLASS
33 //* Virtual method to access the magnetic field
35 virtual void GetFieldValue(const Double_t xyz[], Double_t B[]) const = 0;
37 //* Virtual methods needed for particle transportation
38 //* One can use particular implementations for collider (only Bz component)
39 //* geometry and for fixed-target (CBM-like) geometry which are provided below
40 //* in TRANSPORT section
42 //* Get dS to xyz[] space point
44 virtual Double_t GetDStoPoint( const Double_t xyz[] ) const = 0;
46 //* Get dS to other particle p (dSp for particle p also returned)
48 virtual void GetDStoParticle( const AliKFParticleBase &p,
49 Double_t &DS, Double_t &DSp ) const = 0;
51 //* Transport on dS value along trajectory, output to P,C
53 virtual void Transport( Double_t dS, Double_t P[], Double_t C[] ) const = 0;
67 virtual ~AliKFParticleBase() { ; }
69 //* Initialisation from "cartesian" coordinates ( X Y Z Px Py Pz )
70 //* Parameters, covariance matrix, charge, and mass hypothesis should be provided
72 void Initialize( const Double_t Param[], const Double_t Cov[], Int_t Charge, Double_t Mass );
74 //* Initialise covariance matrix and set current parameters to 0.0
78 //* Set decay vertex parameters for linearisation
80 void SetVtxGuess( Double_t x, Double_t y, Double_t z );
88 Double_t GetX () const { return fP[0]; }
89 Double_t GetY () const { return fP[1]; }
90 Double_t GetZ () const { return fP[2]; }
91 Double_t GetPx () const { return fP[3]; }
92 Double_t GetPy () const { return fP[4]; }
93 Double_t GetPz () const { return fP[5]; }
94 Double_t GetE () const { return fP[6]; }
95 Double_t GetS () const { return fP[7]; }
96 Int_t GetQ () const { return fQ; }
97 Double_t GetChi2 () const { return fChi2; }
98 Int_t GetNDF () const { return fNDF; }
100 Double_t GetParameter ( Int_t i ) const { return fP[i]; }
101 Double_t GetCovariance( Int_t i ) const { return fC[i]; }
102 Double_t GetCovariance( Int_t i, Int_t j ) const { return fC[IJ(i,j)]; }
104 //* Accessors with calculations( &value, &estimated sigma )
105 //* error flag returned (0 means no error during calculations)
107 Int_t GetMomentum ( Double_t &pmom, Double_t &sigmap ) const ;
108 Int_t GetMass ( Double_t &mass, Double_t &sigmam ) const ;
109 Int_t GetDecayLength ( Double_t &dlen, Double_t &sigmal ) const ;
110 Int_t GetLifeTime ( Double_t &tauc, Double_t &sigmat ) const ;
116 Double_t & X () { return fP[0]; }
117 Double_t & Y () { return fP[1]; }
118 Double_t & Z () { return fP[2]; }
119 Double_t & Px () { return fP[3]; }
120 Double_t & Py () { return fP[4]; }
121 Double_t & Pz () { return fP[5]; }
122 Double_t & E () { return fP[6]; }
123 Double_t & S () { return fP[7]; }
124 Int_t & Q () { return fQ; }
125 Double_t & Chi2 () { return fChi2; }
126 Int_t & NDF () { return fNDF; }
128 Double_t & Parameter ( Int_t i ) { return fP[i]; }
129 Double_t & Covariance( Int_t i ) { return fC[i]; }
130 Double_t & Covariance( Int_t i, Int_t j ) { return fC[IJ(i,j)]; }
134 //* CONSTRUCTION OF THE PARTICLE BY ITS DAUGHTERS AND MOTHER
135 //* USING THE KALMAN FILTER METHOD
139 //* Simple way to add daughter ex. D0+= Pion;
141 void operator +=( const AliKFParticleBase &Daughter );
143 //* Add daughter track to the particle
145 void AddDaughter( const AliKFParticleBase &Daughter );
147 //* Set production vertex
149 void SetProductionVertex( const AliKFParticleBase &Vtx );
151 //* Set mass constraint
153 void SetMassConstraint( Double_t Mass, Double_t SigmaMass = 0 );
155 //* Set no decay length for resonances
157 void SetNoDecayLength();
160 //* Everything in one go
162 void Construct( const AliKFParticleBase *vDaughters[], Int_t NDaughters,
163 const AliKFParticleBase *ProdVtx=0, Double_t Mass=-1 );
169 //* ( main transportation parameter is S = SignedPath/Momentum )
170 //* ( parameters of decay & production vertices are stored locally )
174 //* Transport the particle to its decay vertex
176 void TransportToDecayVertex();
178 //* Transport the particle to its production vertex
180 void TransportToProductionVertex();
182 //* Transport the particle on dS parameter (SignedPath/Momentum)
184 void TransportToDS( Double_t dS );
186 //* Particular extrapolators one can use
188 Double_t GetDStoPointBz( Double_t Bz, const Double_t xyz[] ) const;
190 void GetDStoParticleBz( Double_t Bz, const AliKFParticleBase &p,
191 Double_t &dS, Double_t &dS1 ) const ;
193 // Double_t GetDStoPointCBM( const Double_t xyz[] ) const;
195 void TransportBz( Double_t Bz, Double_t dS, Double_t P[], Double_t C[] ) const;
196 void TransportCBM( Double_t dS, Double_t P[], Double_t C[] ) const;
203 //* Calculate distance from another object [cm]
205 Double_t GetDistanceFromVertex( const Double_t vtx[] ) const;
206 Double_t GetDistanceFromVertex( const AliKFParticleBase &Vtx ) const;
207 Double_t GetDistanceFromParticle( const AliKFParticleBase &p ) const;
209 //* Calculate sqrt(Chi2/ndf) deviation from vertex
210 //* v = [xyz], Cv=[Cxx,Cxy,Cyy,Cxz,Cyz,Czz]-covariance matrix
212 Double_t GetDeviationFromVertex( const Double_t v[],
213 const Double_t Cv[]=0 ) const;
214 Double_t GetDeviationFromVertex( const AliKFParticleBase &Vtx ) const;
215 Double_t GetDeviationFromParticle( const AliKFParticleBase &p ) const;
217 //* Subtract the particle from the vertex
219 void SubtractFromVertex( Double_t v[], Double_t Cv[],
220 Double_t &vChi2, Int_t vNDF ) const ;
224 static Int_t IJ( Int_t i, Int_t j ){
225 return ( j<=i ) ? i*(i+1)/2+j :j*(j+1)/2+i;
228 Double_t & Cij( Int_t i, Int_t j ){ return fC[IJ(i,j)]; }
230 void Convert( bool ToProduction );
231 void TransportLine( Double_t S, Double_t P[], Double_t C[] ) const ;
232 Double_t GetDStoPointLine( const Double_t xyz[] ) const;
234 static void MultQSQt( const Double_t Q[], const Double_t S[],
237 void GetMeasurement( const Double_t XYZ[], Double_t m[], Double_t V[] ) const ;
239 Double_t fP[8]; //* Main particle parameters {X,Y,Z,Px,Py,Pz,E,S[=DecayLength/P]}
240 Double_t fC[36]; //* Low-triangle covariance matrix of fP
241 Int_t fQ; //* Particle charge
242 Int_t fNDF; //* Number of degrees of freedom
243 Double_t fChi2; //* Chi^2
245 Double_t fSFromDecay; //* Distance from decay vertex to current position
247 Bool_t fAtProductionVertex; //* Flag shows that the particle error along
248 //* its trajectory is taken from production vertex
250 Double_t fVtxGuess[3]; //* Guess for the position of the decay vertex
251 //* ( used for linearisation of equations )
253 Bool_t fIsLinearized; //* Flag shows that the guess is present
255 ClassDef( AliKFParticleBase, 1 );