// -------------------------------------------------------------------------
// -----             CbmPolarizedGenerator header file                 -----
// -----              Created 11/09/09  by E. Kryshen                  -----
// -------------------------------------------------------------------------

/** CbmPolarizedGenerator.h
 ** @author Evgeny Kryshen <e.kryshen@gsi.de>
 **
 ** CbmPolarizedGenerator generates polarized vector mesons with a given
 ** distribution over pt [ dn/dpt = pt*exp(-mt/T) ]
 ** and rapidity (Gaussian) with fixed multiplicity per event.
 ** Mesons are forced to decay via dielectron or dimuon channel.
 
 ** Decay products are distributed as follows:
 ** d sigma / d cos theta ~ 1 + alpha*(cos theta)^2
 ** 
 ** One can set polarization parameter alpha in helicity or Collins-Soper 
 ** reference frame.
 
 ** Derived from FairGenerator.
 */


#ifndef CBMPOLARIZEDGENERATOR_H
#define CBMPOLARIZEDGENERATOR_H

#include "FairGenerator.h"
#include "TF1.h"
#include "TVector3.h"

using namespace std;

class FairPrimaryGenerator;

class CbmPolarizedGenerator : public FairGenerator
{
public:
  typedef enum { kNoPol = 0, kColSop = 1, kHelicity = 2} Frame_t;
  typedef enum { kDiElectron = 1, kDiMuon = 2} DecayMode_t;
  
  /** Default constructor. */
  CbmPolarizedGenerator();

  /** Constructor with PDG-ID, multiplicity
   **@param pdgid Particle type (PDG encoding)
   **@param mult  Multiplicity (default is 1)
   **/
  CbmPolarizedGenerator(Int_t pdgid, Int_t mult=1);

  /** Destructor */
  virtual ~CbmPolarizedGenerator() {};

  Bool_t GenerateDaughters(const TVector3 p, FairPrimaryGenerator* primGen);
  
  /** Modifiers */
  inline void SetPDGType        (Int_t pdg)  {fPDGType = pdg;  };
  inline void SetMultiplicity   (Int_t mult) {fMult    = mult; };
  
  // Set temperature for transverse momentum distribution in GeV
  inline void SetDistributionPt (Double_t T=0.154319, Double_t mass=-1.) {fT=T; fPtDistMass=mass;};
  
  // Set rapidity distribution parameters (y0 - mid rapidity, sigma - Gaussian width)
  inline void SetDistributionY  (Double_t y0=1.98604, Double_t sigma=0.617173) {fY0=y0;fSigma=sigma;};
  
  // Set range
  inline void SetRangePt        (Double_t ptMin=0, Double_t ptMax=3) {fPtMin=ptMin;fPtMax=ptMax;};
  inline void SetRangeY         (Double_t yMin=0, Double_t yMax=4) {fYMin=yMin;fYMax=yMax;};

  // Set polarization parameter
  inline void SetAlpha(Double_t alpha=0)                  {fAlpha=alpha;}

  /** Set reference frame for polarization calculation
   * @param frame = kColSop - Collins-Soper/ kHelicity - Helicity
   */
  inline void SetRefFrame(Frame_t frame=kColSop)          {fFrame=frame;}
  
  /** Set decay mode (kDiMuon/kDiElectron) */
  inline void SetDecayMode(DecayMode_t decayMode=kDiMuon) {fDecayMode=decayMode;}
  
  /** Set beam momentum (used in Collins-Soper reference frame)
  /* @param mom  beam momentum in GeV/c 
   **/
  inline void SetBeamMomentum(Double_t mom)               {fBeamMomentum = mom;}
  
  /** Set box generator - flat distributions in rapidity and pt
  /* @param box = 1 - box, 0 - thermal
   */ 
  inline void SetBox(Bool_t box)                          {fBox = box;}
  
  /** Initializer */
  Bool_t Init();

  /** Creates an event with given type and multiplicity.
   * @param primGen  pointer to the CbmPrimaryGenerator
   */
  virtual Bool_t ReadEvent(FairPrimaryGenerator* primGen);

private:
  Int_t    fPDGType;      ///< Particle type (PDG encoding)
  Int_t    fMult;         ///< Multiplicity
  Double_t fT;            ///< Temperature in the Pt distribution
  Double_t fPtDistMass;   ///< Mass in Pt distribution
  Double_t fY0;           ///< Mean rapidity
  Double_t fSigma;        ///< Simga in the rapidity distribution
  Double_t fPtMin;        ///< Max value of Pt
  Double_t fPtMax;        ///< Min value of Pt
  Double_t fYMin;        ///< Max value of Pt
  Double_t fYMax;        ///< Min value of Pt
  Double_t fPDGMass;      ///< Particle mass [GeV]
  TF1*     fDistPt;       //! Pointer to the Pt function
  Double_t fAlpha;        //< Polarization parameter in the helicity frame
  Frame_t     fFrame;     //< Choice of decay products
  DecayMode_t fDecayMode; //< Reference system for polarization  
  Double_t fBeamMomentum; //< Beam momentum in lab frame
  TF1*     fPol;          //! Polarization function
  Bool_t   fBox;          // fBox = 1 Box generator, fBox = 0 - termal pt and gaussian y 

  CbmPolarizedGenerator(const CbmPolarizedGenerator&);
  CbmPolarizedGenerator operator=(const CbmPolarizedGenerator&);

  ClassDef(CbmPolarizedGenerator,1);
};

#endif