RICH/AliRICHHelix.h

   1 #ifndef AliRICHHelix_h
   2 #define AliRICHHelix_h
   3
   4 #include <TObject.h>              //base class
   5 #include <TVector3.h>             //used extensively
   6 #include "AliRICHParam.h"         //RichIntersect()
   7
   8 class AliRICHHelix: public TObject
   9 {
  10 public:
  11   AliRICHHelix():TObject(),
  12     fX0(TVector3(0,0,0)),
  13     fP0(TVector3(0,0,0)),
  14     fX(TVector3(0,0,0)),
  15     fP(TVector3(0,0,0)),
  16     fLen(0),
  17     fQ(0),
  18     fBz(0),
  19     fPosRad(TVector2(0,0)),
  20     fPosPc(TVector2(0,0)),
  21     fPloc(TVector3(0,0,0))            {}
  22   AliRICHHelix(Double_t p,Double_t theta,Double_t phi,Double_t bz=0.2);//p [GeV], theta,phi [deg], Bz [Tesla];
  23   AliRICHHelix(const TVector3 &x0,const TVector3 &p0,Int_t q=1,Double_t b=0.2):TObject(),
  24     fX0(x0),
  25     fP0(p0),
  26     fX(x0),
  27     fP(p0),
  28     fLen(0),
  29     fQ(q),
  30     fBz(b),
  31     fPosRad(TVector2(0,0)),
  32     fPosPc(TVector2(0,0)),
  33     fPloc(TVector3(0,0,0))            {}
  34   virtual ~AliRICHHelix()                                                                                                                   {}
  35
  36          void     Draw          (const Option_t *opt=""              );                              //from TObject, draw helix
  37          void     Print         (const Option_t *opt=""              )const;                         //from TObject, print status
  38 //private part++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  39   inline Bool_t   Intersection  (TVector3 planePnt,TVector3 planeNorm);                              //intersection with plane given by point and normal vector
  40   inline void     Propagate     (Double_t len                        );                              //propogate helix by given length along it
  41   inline Int_t    RichIntersect (AliRICHParam *pParam                );                              //search intersection with any RICH chamber
  42          TVector2 PosRad        (                                    )const{return fPosRad;}         //intersection with radiator LORS
  43          TVector2 PosPc         (                                    )const{return fPosPc;}          //returns position of intersection with PC (local system)
  44          TVector3 Ploc          (                                    )const{return fPloc;}           //returns momentum at the position of intersection with radiator
  45 //         Double_t Length        ()                const{return fLen;}             //returns length of the track from initial point to RICH
  46          TVector3 X             (                                    )const{return fX;}
  47 protected:
  48   TVector3 fX0;            //helix position in point of definition, [cm]    in MARS
  49   TVector3 fP0;            //helix momentum in point of definition, [GeV/c] in MARS
  50   TVector3 fX;             //helix position in point of interest,  [cm]    in MARS
  51   TVector3 fP;             //helix momentum in point of interest,  [GeV/c] in MARS
  52   Double_t fLen;           //helix length from point of definition to point of interest, [cm]
  53   Int_t    fQ;             //sign of track charge (value not provided by current ESD)
  54   Double_t fBz;            //magnetic field along z, [Tesla]
  55   TVector2 fPosRad;        //helix intersection with radiator entrance, LORS [cm]
  56   TVector2 fPosPc;         //helix intersection with PC, LORS [cm]
  57   TVector3 fPloc;          //helix momentum, LORS [GeV/c]
  58   ClassDef(AliRICHHelix,0) //General helix
  59 };//class AliRICHHelix
  60 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  61 void AliRICHHelix::Propagate(Double_t len)
  62 {
  63 // Propogates the helix from inintial point by a given distance along helix. Assumes uniform magnetic field along z direction.
  64 // Arguments: len - distance to propagate by, [cm]
  65 //   Returns: none
  66   if(fBz==0){//no magnetic field->straight line
  67     fX=fX0+fP0.Unit()*len;
  68   }else{
  69     const Double_t c = 0.00299792458;//this speed of light value provides that coordinates are in cm momentum in GeV/c
  70     Double_t a = -c*fBz*fQ;
  71      Double_t rho = a/fP0.Mag();
  72     fX.SetX( fX0.X()+fP0.X()*TMath::Sin(rho*len)/a-fP0.Y()*(1-TMath::Cos(rho*len))/a  );
  73     fX.SetY( fX0.Y()+fP0.Y()*TMath::Sin(rho*len)/a+fP0.X()*(1-TMath::Cos(rho*len))/a  );
  74     fX.SetZ( fX0.Z()+fP0.Z()*len/fP0.Mag()                                            );
  75     fP.SetX( fP0.X()*TMath::Cos(rho*len)-fP0.Y()*TMath::Sin(rho*len)                  );
  76     fP.SetY( fP0.Y()*TMath::Cos(rho*len)+fP0.X()*TMath::Sin(rho*len)                  );
  77     fP.SetZ( fP0.Z()                                                                  );
  78     fLen=len;
  79   }
  80 }
  81 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  82 Bool_t AliRICHHelix::Intersection(TVector3 planePoint,TVector3 planeNorm)
  83 {
  84 // Finds point of intersection (if exists) of the helix with the plane. Stores result in fX and fP.
  85 // Arguments: planePoint,planeNorm - the plane defined by any plane's point and vector, normal to the plane
  86 //   Returns: kTrue if helix intersects the plane, kFALSE otherwise.
  87
  88   Double_t s=(planePoint-fX0)*planeNorm,dist=99999,distPrev=dist;//estimates initial distance to plane
  89
  90   while(TMath::Abs(dist)>0.00001){
  91     Propagate(s);                        //calculates helix at the distance s from x0 ALONG the helix
  92     dist=(fX-planePoint)*planeNorm;      //distance between current helix position and plane
  93     if(TMath::Abs(dist) >= TMath::Abs(distPrev)) { return kFALSE;}
  94     distPrev=dist;
  95     s-=dist;
  96   }
  97   return kTRUE;
  98 }
  99 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 100 Int_t AliRICHHelix::RichIntersect(AliRICHParam *pParam)
 101 {
 102 // Searchs for intersection of this helix with all RICH chambers, returns chamber number or 0 if no intersection
 103 // On exit fPosRad contain position of intersection in radiator LORS (cm)
 104 //         fPosPc  contains the same for photocathode
 105   for(Int_t iCh=1;iCh<=AliRICHParam::kNch;iCh++){//chambers loop
 106     TVector3 norm =pParam->Lors2MarsVec(iCh,TVector3(0,0,1));
 107     if(Intersection(pParam->Lors2Mars(iCh,0,0,AliRICHParam::kRad),norm)){//there is intersection with radiator plane
 108       fPosRad=pParam->Mars2Lors(iCh,fX,AliRICHParam::kRad);//position on radiator plane
 109       if(pParam->IsAccepted(fPosRad)){//intersection within radiator (even if in dead zone)
 110
 111         if(Intersection(pParam->Lors2Mars(iCh,0,0,AliRICHParam::kPc),norm)){//there is intersection with photocathode
 112           fPosPc=pParam->Mars2Lors(iCh,fX,AliRICHParam::kPc);//position on radiator plane
 113           if(pParam->IsAccepted(fPosPc)){//intersection within pc (even if in dead zone)
 114
 115             fPloc=pParam->Mars2LorsVec(iCh,fP);//trasform p to local system
 116             return iCh;
 117           }//if inside PC
 118         }//if intersects PC
 119
 120       }//if inside radiator
 121     }//if for radiator
 122   }//chambers loop
 123   return 0;
 124 }
 125 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 126 #endif