//--------------------------------------------------------------------------
// File and Version Information:
//  $Id: RhoFindOmittedParticle.h,v 1.1.1.1 2001-05-04 16:20:06 marcel Exp $
//
// Description:
//  Class RhoFindOmittedParticle.
//  Given resonance (Y(4S)) momentum, B0 momentum, and
//  K0L mass at creation, this object then finds the best
//  candidate for the K0L 4-momentum given the 4-momentum
//  of the J/psi and the direction of the neutral cluster.
//
//  Because this is a general utility class, B0 is labeled Child,
//  Y(4S) is labeled Reson (for Resonance), J/psi is labeled Obs
//  (for Observed), and K0L is labeled Sought (for the calculated
//  values) or Seen (for the actual IFR/EMC cluster).
//
//  Constructor takes CM 4-momentum, Child mass, and Sought mass.
//
//  fitToSeen() calls makeCone(), then closestFit().
//
//  makeCone() finds the possible Sought 4-momenta given the Observed
//  momentum.
//
//  closestFit() finds the best fit between the cone of possibilities
//  and the Seen neutral cluster.
//
//  secondVector() returns the second momentum found by closestFit()
//  but rejected as an inferior fit, for diagnostic purposes.
//
//  If there is demand, a function may be added to extract the
//  parameters of the cone describing possible Sought momenta;
//  makeCone() and closestFit() would then be made public;
//  or perhaps a subclass could implement this functionality.
//
//  Note: this class by default currently only works in
//  coordinate systems with the boost along the z-axis.
//  Setting zBoostApprox to false overrides this.
//  Note: this class currently assumes (as is the case for B0->J/psi KL)
//  that in the resonance CM (Y(4S)) frame, the 3-momentum of the
//  observed (J/psi) particle is much larger than the child (B0)
//  3-momentum, insuring that the CM angle between the observed and
//  sought (KL) is greater than pi/2.  (In the language of this class,
//  openCos>0, since we use the opposite of the observed momentum).
//
// Environment:
//  Software developed for the BaBar Detector at the SLAC B-Factory.
//
// Author List:
//      Adam Breon                      Original Author
//
// Copyright Information:
//  Copyright (C) 1997-1999   Lawrence Berkeley Laboratory
//
// ROOT Version by Marcel Kunze, RUB
// Ralf Kliemt, HIM/GSI Feb.2013 (Cleanup & Restructuring)              
//------------------------------------------------------------------------

#ifndef RHOFINDOMITTEDPARTICLE_H
#define RHOFINDOMITTEDPARTICLE_H

#include "TVector3.h"
#include "TLorentzVector.h"

class RhoFindOmittedParticle : public TObject
{

//--------------------
// Instance Members --
//--------------------

  public:

    // Constructors
    RhoFindOmittedParticle (
      const TLorentzVector& ip4Reson,  // set Y(4S) p4, usually.
      const double imChild,   // B0 mass.
      const double imSought,    // K mass (p4 not known).
      const Bool_t izBoostApprox=kTRUE ); // Approximate boost along z?

    virtual ~RhoFindOmittedParticle( );

    TLorentzVector FitToSeen ( const TLorentzVector& p4Obs,
                               const TVector3& p3Seen );

    // Returns the second-choice fit vector.
    TLorentzVector SecondVector( ) const;

  protected:

    void MakeCone ( const TLorentzVector& p4Obs );

    TLorentzVector ClosestFit ( const TVector3& p3Seen );

    //TLorentzVector p4Reson;   // 4-momentum of resonance
    //float mChild;     // mass of Child
    float mSought2;     //! squared mass of Sought

    Bool_t zBoostApprox;      //! Flag: do we approximate boost in
    // the z direction, or use real boost?
    // (Default = kTRUE).

    float cmEChild, cmpChild2;    //! energy, squared 3-momentum of Child.

    //Caches value of p4Obs to avoid recalculating the code unnecessarily.
    TLorentzVector p4ObsCache; //!

    //Stores value of worse fit so we can look at it.
    TLorentzVector secondChoice;  //! The _other_ vector, stored.

    // BOOST vectors.
    TVector3  beta;     //! From lab to CM (-beta CM to lab)

    // The cone parameters.
    TVector3  cmAxis;     //! Axis of CM cone
    double        openCos;    //! cos of opening angle.
    double  cmESought;    //! CM energy of sought particle.
    double  cmpSought2;   //! square of CM 3-momentum of sought.

  public:
    ClassDef ( RhoFindOmittedParticle,1 ) // Finds the best candidate for the K0L 4-momentum
};
#endif