RhoFindOmittedParticle.h

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//*                 copied verbatim in the file "LICENSE".                   *
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//*  Copyright (C) 2006 - 2024 FAIR GmbH and copyright holders of PandaRoot  *
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//--------------------------------------------------------------------------
// 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; 

  Bool_t zBoostApprox; 
  // the z direction, or use real boost?
  // (Default = kTRUE).

  float cmEChild, cmpChild2; 

  // 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; 

  // BOOST vectors.
  TVector3 beta; 

  // The cone parameters.
  TVector3 cmAxis;   
  double openCos;    
  double cmESought;  
  double cmpSought2; 

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