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