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 //* Initialise covariance matrix and set current parameters to 0.0
73 //* Set decay vertex parameters for linearisation
75 void SetVtxGuess( Double_t x, Double_t y, Double_t z );
83 Double_t GetX () const { return fP[0]; }
84 Double_t GetY () const { return fP[1]; }
85 Double_t GetZ () const { return fP[2]; }
86 Double_t GetPx () const { return fP[3]; }
87 Double_t GetPy () const { return fP[4]; }
88 Double_t GetPz () const { return fP[5]; }
89 Double_t GetE () const { return fP[6]; }
90 Double_t GetS () const { return fP[7]; }
91 Int_t GetQ () const { return fQ; }
92 Double_t GetChi2 () const { return fChi2; }
93 Int_t GetNDF () const { return fNDF; }
95 Double_t GetParameter ( Int_t i ) const { return fP[i]; }
96 Double_t GetCovariance( Int_t i ) const { return fC[i]; }
97 Double_t GetCovariance( Int_t i, Int_t j ) const { return fC[IJ(i,j)]; }
99 //* Accessors with calculations( &value, &estimated sigma )
100 //* error flag returned (0 means no error during calculations)
102 Int_t GetMomentum ( Double_t &P, Double_t &SigmaP ) const ;
103 Int_t GetMass ( Double_t &M, Double_t &SigmaM ) const ;
104 Int_t GetDecayLength ( Double_t &L, Double_t &SigmaL ) const ;
105 Int_t GetLifeTime ( Double_t &T, Double_t &SigmaT ) const ;
111 Double_t & X () { return fP[0]; }
112 Double_t & Y () { return fP[1]; }
113 Double_t & Z () { return fP[2]; }
114 Double_t & Px () { return fP[3]; }
115 Double_t & Py () { return fP[4]; }
116 Double_t & Pz () { return fP[5]; }
117 Double_t & E () { return fP[6]; }
118 Double_t & S () { return fP[7]; }
119 Int_t & Q () { return fQ; }
120 Double_t & Chi2 () { return fChi2; }
121 Int_t & NDF () { return fNDF; }
123 Double_t & Parameter ( Int_t i ) { return fP[i]; }
124 Double_t & Covariance( Int_t i ) { return fC[i]; }
125 Double_t & Covariance( Int_t i, Int_t j ) { return fC[IJ(i,j)]; }
129 //* CONSTRUCTION OF THE PARTICLE BY ITS DAUGHTERS AND MOTHER
130 //* USING THE KALMAN FILTER METHOD
134 //* Simple way to add daughter ex. D0+= Pion;
136 void operator +=( const AliKFParticleBase &Daughter );
138 //* Add daughter track to the particle
140 void AddDaughter( const AliKFParticleBase &Daughter );
142 //* Set production vertex
144 void SetProductionVertex( const AliKFParticleBase &Vtx );
146 //* Set hard mass constraint
148 void SetMassConstraint( Double_t Mass );
150 //* Everything in one go
152 void Construct( const AliKFParticleBase *vDaughters[], Int_t NDaughters,
153 const AliKFParticleBase *ProdVtx=0, Double_t Mass=-1 );
159 //* ( main transportation parameter is S = SignedPath/Momentum )
160 //* ( parameters of decay & production vertices are stored locally )
164 //* Transport the particle to its decay vertex
166 void TransportToDecayVertex();
168 //* Transport the particle to its production vertex
170 void TransportToProductionVertex();
172 //* Transport the particle on dS parameter (SignedPath/Momentum)
174 void TransportToDS( Double_t dS );
176 //* Particular extrapolators one can use
178 Double_t GetDStoPointBz( Double_t Bz, const Double_t xyz[] ) const;
180 void GetDStoParticleBz( Double_t Bz, const AliKFParticleBase &p,
181 Double_t &dS, Double_t &dS1 ) const ;
183 // Double_t GetDStoPointCBM( const Double_t xyz[] ) const;
185 void TransportBz( Double_t Bz, Double_t dS, Double_t P[], Double_t C[] ) const;
186 void TransportCBM( Double_t dS, Double_t P[], Double_t C[] ) const;
193 //* Calculate distance from another object [cm]
195 Double_t GetDistanceFromVertex( const Double_t vtx[] ) const;
196 Double_t GetDistanceFromVertex( const AliKFParticleBase &Vtx ) const;
197 Double_t GetDistanceFromParticle( const AliKFParticleBase &p ) const;
199 //* Calculate sqrt(Chi2/ndf) deviation from vertex
200 //* v = [xyz], Cv=[Cxx,Cxy,Cyy,Cxz,Cyz,Czz]-covariance matrix
202 Double_t GetDeviationFromVertex( const Double_t v[],
203 const Double_t Cv[]=0 ) const;
204 Double_t GetDeviationFromVertex( const AliKFParticleBase &Vtx ) const;
205 Double_t GetDeviationFromParticle( const AliKFParticleBase &p ) const;
207 //* Subtract the particle from the vertex
209 void SubtractFromVertex( Double_t v[], Double_t Cv[],
210 Double_t &vChi2, Int_t vNDF ) const ;
214 static Int_t IJ( Int_t i, Int_t j ){
215 return ( j<=i ) ? i*(i+1)/2+j :j*(j+1)/2+i;
218 Double_t & Cij( Int_t i, Int_t j ){ return fC[IJ(i,j)]; }
220 void Convert( bool ToProduction );
221 void TransportLine( Double_t S, Double_t P[], Double_t C[] ) const ;
222 Double_t GetDStoPointLine( const Double_t xyz[] ) const;
224 static void MultQSQt( const Double_t Q[], const Double_t S[],
227 void GetMeasurement( const Double_t XYZ[], Double_t m[], Double_t V[] ) const ;
229 Double_t fP[8]; //* Main particle parameters {X,Y,Z,Px,Py,Pz,E,S[=DecayLength/P]}
230 Double_t fC[36]; //* Low-triangle covariance matrix of fP
231 Int_t fQ; //* Particle charge
232 Int_t fNDF; //* Number of degrees of freedom
233 Double_t fChi2; //* Chi^2
235 Double_t fSFromDecay; //* Distance from decay vertex to current position
237 Bool_t fAtProductionVertex; //* Flag shows that the particle error along
238 //* its trajectory is taken from production vertex
240 Double_t fVtxGuess[3]; //* Guess for the position of the decay vertex
241 //* ( used for linearisation of equations )
243 Bool_t fIsLinearized; //* Flag shows that the guess is present
245 ClassDef( AliKFParticleBase, 1 );