RICH/AliRICHHelix.h

   1 #ifndef AliRICHHelix_h
   2 #define AliRICHHelix_h
   3
   4 #include <TObject.h>
   5 #include <TVector3.h>
   6 #include "AliRICHParam.h"
   7 #include "AliRICHChamber.h"
   8
   9 class AliRICHHelix: public TObject
  10 {
  11 public:
  12   AliRICHHelix():TObject()                                                                                                          {;}
  13   AliRICHHelix(const TVector3 &x0,const TVector3 &p0,Int_t q=1,Double_t b=0.2):TObject(),fX0(x0),fP0(p0),fX(x0),fP(p0),
  14                                                                                          fLen(0),fQ(q),fBz(b)                       {;}
  15   virtual ~AliRICHHelix()                                                                                                           {;}
  16
  17   inline void     Propagate(Double_t len);                                          //propogate helix by length len along it
  18   inline Int_t    RichIntersect(AliRICHParam *pParam);                              //search intersection with any RICH chamber
  19   inline Bool_t   Intersection(TVector3 planePnt,TVector3 planeNorm);               //intersection with plane given by point and normal vector
  20          Bool_t   Intersection(TVector3 pl)    {return Intersection(pl,pl.Unit());} // special plane given by point only
  21          TVector2 PosRad()                const{return fPosRad;}          //returns position of intersection with radiator (local system)
  22          TVector2 PosAnod()               const{return fPosAnod;}         //returns position of intersection with anod wires plane (local system)
  23          TVector2 PosPc()                 const{return fPosPc;}           //returns position of intersection with PC (local system)
  24          TVector3 Ploc()                  const{return fPloc;}            //returns momentum at the position of intersection with radiator
  25          void     Print(Option_t *sOption)const; //virtual interface from TObject
  26 protected:
  27   TVector3 fX0;            //helix position in parametrised point, cm    in MRS
  28   TVector3 fP0;            //helix momentum in parametrised point, GeV/c in MRS
  29   TVector3 fX;             //helix position in point of interest,  cm    in MRS
  30   TVector3 fP;             //helix momentum in point of interest,  GeV/c in MRS
  31   Double_t fLen;           //helix length in point of interest
  32   Int_t    fQ;             //sign of track charge (value not provided by current ESD)
  33   Double_t fBz;            //magnetic field along z value in Tesla under assumption of uniformity
  34   TVector2 fPosRad;        //track intersection with radiator (local system)
  35   TVector2 fPosAnod;       //track intersection with anod wires plane (local system)
  36   TVector2 fPosPc;         //track intersection with PC (local system)
  37   TVector3 fPloc;          //momentum in local system
  38   ClassDef(AliRICHHelix,0) //General helix
  39 };//class AliRICHHelix
  40 //__________________________________________________________________________________________________
  41 void AliRICHHelix::Propagate(Double_t len)
  42 {
  43 // Propogates the helix to the position of interest defined by helix length s
  44 // Assumes uniform magnetic field along z direction.
  45   const Double_t c = 0.00299792458;//this value provides that coordinates are in cm momentum in GeV/c
  46   Double_t a = -c*fBz*fQ;
  47
  48   Double_t rho = a/fP0.Mag();
  49   fX.SetX( fX0.X()+fP0.X()*TMath::Sin(rho*len)/a-fP0.Y()*(1-TMath::Cos(rho*len))/a  );
  50   fX.SetY( fX0.Y()+fP0.Y()*TMath::Sin(rho*len)/a+fP0.X()*(1-TMath::Cos(rho*len))/a  );
  51   fX.SetZ( fX0.Z()+fP0.Z()*len/fP0.Mag()                                            );
  52   fP.SetX( fP0.X()*TMath::Cos(rho*len)-fP0.Y()*TMath::Sin(rho*len)                  );
  53   fP.SetY( fP0.Y()*TMath::Cos(rho*len)+fP0.X()*TMath::Sin(rho*len)                  );
  54   fP.SetZ( fP0.Z()                                                                  );
  55   fLen=len;
  56 }
  57 //__________________________________________________________________________________________________
  58 Bool_t AliRICHHelix::Intersection(TVector3 planePoint,TVector3 planeNorm)
  59 {
  60 // Finds point of intersection (if exists) of the helix to the plane given by point and normal vector.
  61 // Returns kTrue if helix intersects the plane, kFALSE otherwise.
  62 // Stores result in current helix fields fX and fP.
  63
  64   Double_t s=(planePoint-fX0)*planeNorm,dist=99999,distPrev=dist;//estimates initial distance to plane
  65
  66   while(TMath::Abs(dist)>0.00001){
  67     Propagate(s);                        //calculates helix at the distance s from x0 ALONG the helix
  68     dist=(fX-planePoint)*planeNorm;      //distance between current helix position and plane
  69     if(TMath::Abs(dist) >= TMath::Abs(distPrev)) { return kFALSE;}
  70     distPrev=dist;
  71     s-=dist;
  72   }
  73   return kTRUE;
  74 }
  75 //__________________________________________________________________________________________________
  76 Int_t AliRICHHelix::RichIntersect(AliRICHParam *pParam)
  77 {
  78 // Searchs for intersection of this helix with all RICH chambers, returns chamber number or 0 if no intersection
  79 // On exit fPosRad contain position of intersection in Local System with radiator
  80 //         fPosPc  contains the same for photocathode
  81   for(Int_t iChamberN=1;iChamberN<=kNchambers;iChamberN++){//chamber loop
  82     if(Intersection(pParam->C(iChamberN)->Rad())){//there is intersection with radiator plane
  83       fPosRad=pParam->C(iChamberN)->Mrs2Rad(fX);//position on radiator plane
  84       if(pParam->IsAccepted(fPosRad)){//intersection within radiator (even if in dead zone)
  85
  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
  90             Intersection(pParam->C(iChamberN)->Anod()); //search for anod intersection position
  91             fPosAnod=pParam->C(iChamberN)->Mrs2Anod(fX);
  92
  93             fPloc=pParam->C(iChamberN)->PMrs2Loc(fP);//trasform p to local system
  94             return iChamberN;
  95           }//if inside PC
  96         }//if intersects PC
  97
  98       }//if inside radiator
  99     }//if for radiator
 100   }//chamber loop
 101   return 0;
 102 }
 103 //__________________________________________________________________________________________________
 104 #endif