6 #include "AliRICHParam.h"
7 #include "AliRICHChamber.h"
9 class AliRICHHelix: public TObject
13 AliRICHHelix(TVector3 x0,TVector3 p0,Int_t q,Double_t b=0.4) {fX0=x0;fP0=p0;fQ=q;fBz=b;} //takes position and momentum at parametrised point
14 virtual ~AliRICHHelix() {;}
15 inline void Propagate(Double_t lenght);
16 Bool_t Intersection(TVector3 plane) {return Intersection(plane,plane.Unit());} // special plane given by point only
17 inline Bool_t Intersection(TVector3 planePoint,TVector3 planeNorm); //intersection with plane given by point and normal vector
18 inline Int_t RichIntersect(AliRICHParam *pParam);
19 TVector3 X()const {return fX;}
20 TVector3 P()const {return fP;}
21 TVector3 X0()const {return fX0;}
22 TVector3 P0()const {return fP0;}
23 TVector2 PosPc() const {return fPosPc;} //returns position of intersection with PC
24 TVector2 PosRad()const {return fPosRad;} //returns position of intersection with radiator
25 TVector3 Ploc()const {return fPloc;} //returns momentum at the position of intersection with radiator
27 void Print(Option_t *sOption)const; //virtual interface from TObject
29 TVector3 fX0; //helix position in parametrised point, cm in MRS
30 TVector3 fP0; //helix momentum in parametrised point, GeV/c in MRS
31 TVector3 fX; //helix position in point of interest, cm in MRS
32 TVector3 fP; //helix momentum in point of interest, GeV/c in MRS
33 Double_t fLength; //helix length in point of interest
34 Int_t fQ; //sign of track charge (value not provided by current ESD)
35 Double_t fBz; //magnetic field along z value in Tesla under assumption of uniformity
36 TVector2 fPosPc; //position on PC in local system
37 TVector2 fPosRad; //position on radiator in local system
38 TVector3 fPloc; //momentum in local system
39 ClassDef(AliRICHHelix,0) //General helix
40 };//class AliRICHHelix
41 //__________________________________________________________________________________________________
42 void AliRICHHelix::Propagate(Double_t length)
44 // Propogates the helix to the position of interest defined by helix length s
45 // Assumes uniform magnetic field along z direction.
46 const Double_t c = 0.00299792458;//this value provides that coordinates are in cm momentum in GeV/c
47 Double_t a = -c*fBz*fQ;
49 Double_t rho = a/fP0.Mag();
50 fX.SetX( fX0.X()+fP0.X()*TMath::Sin(rho*length)/a-fP0.Y()*(1-TMath::Cos(rho*length))/a );
51 fX.SetY( fX0.Y()+fP0.Y()*TMath::Sin(rho*length)/a+fP0.X()*(1-TMath::Cos(rho*length))/a );
52 fX.SetZ( fX0.Z()+fP0.Z()*length/fP0.Mag() );
53 fP.SetX( fP0.X()*TMath::Cos(rho*length)-fP0.Y()*TMath::Sin(rho*length) );
54 fP.SetY( fP0.Y()*TMath::Cos(rho*length)+fP0.X()*TMath::Sin(rho*length) );
58 //__________________________________________________________________________________________________
59 Bool_t AliRICHHelix::Intersection(TVector3 planePoint,TVector3 planeNorm)
61 // Finds point of intersection (if exists) of the helix to the plane given by point and normal vector.
62 // Returns kTrue if helix intersects the plane, kFALSE otherwise.
63 // Stores result in current helix fields fX and fP.
65 Double_t s=(planePoint-fX0)*planeNorm,dist=99999,distPrev=dist;
67 while(TMath::Abs(dist)>0.0001){
68 Propagate(s); //calculates helix at the distance s from x0 ALONG the helix
69 dist=(fX-planePoint)*planeNorm; //distance between current helix position and plane
70 if(TMath::Abs(dist) >= TMath::Abs(distPrev)) { return kFALSE;}
76 //__________________________________________________________________________________________________
77 Int_t AliRICHHelix::RichIntersect(AliRICHParam *pParam)
79 // Searchs for intersection of this helix with all RICH chambers, returns chamber number or 0 if no intersection
80 // On exit fPosRad contain position of intersection in Local System with radiator
81 // fPosPc contains the same for photocathode
82 for(Int_t iChamberN=1;iChamberN<=kNchambers;iChamberN++){//chamber loop
83 if(Intersection(pParam->C(iChamberN)->Rad())){//there is intersection with radiator plane
84 fPosRad=pParam->C(iChamberN)->Mrs2Rad(fX);//position on radiator plane
85 if(pParam->IsAccepted(fPosRad)){//intersection within radiator (even if in dead zone)
86 if(Intersection(pParam->C(iChamberN)->Pc())){//there is intersection with photocathode
87 fPosPc=pParam->C(iChamberN)->Mrs2Pc(fX);//position on photcathode plane
88 if(pParam->IsAccepted(fPosPc)){//intersection within pc (even if in dead zone)
89 fPloc=pParam->C(iChamberN)->PMrs2Loc(fP);
98 //__________________________________________________________________________________________________