libthepeg-dev 1.8.0-1.1 / usr / include / ThePEG / Helicity / RSFermionSpinInfo.h

// -*- C++ -*-
//
// RSFermionSpinInfo.h is a part of ThePEG - Toolkit for HEP Event Generation
// Copyright (C) 2003-2011 Peter Richardson, Leif Lonnblad
//
// ThePEG is licenced under version 2 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
#ifndef THEPEG_RSFermionSpinInfo_H
#define THEPEG_RSFermionSpinInfo_H
// This is the declaration of the RSFermionSpinInfo class.

#include "ThePEG/EventRecord/SpinInfo.h"
#include "ThePEG/Helicity/LorentzRSSpinor.h"
#include "RSFermionSpinInfo.fh"

namespace ThePEG {
namespace Helicity {

/**
 *  The RSFermionSpinInfo class inherits from the SpinInfo class and
 *  implements the storage of the basis vector for a spin-3/2 particle.
 *  The basis states are the vector u spinors for a particle and the vector
 *  v-spinors for an antiparticle. The barred spinors can be obtained from these.
 *
 *  These basis states should be set by either the matrixelements or decayers
 *  which are capable of generating spin correlation information.
 *
 *  The basis states in the rest frame of the particles can then be accessed by
 *  the decayers to produce the correct correlations.
 *
 *  N.B. in our convention 0 is the \f$-\frac32\f$ helicity state,
 *  1 is the \f$-\frac12\f$ helicity state,
 *  2 is the \f$+\frac12\f$ helicity state,
 *  3 is the \f$+\frac32\f$ helicity state.
 *
 * @see SpinInfo
 *
 * \author Peter Richardson
 *
 */
class RSFermionSpinInfo: public SpinInfo {

public:

  /** @name Standard constructors and destructors. */
  //@{
  /**
   * Default constructor.
   */
  RSFermionSpinInfo()  : SpinInfo(PDT::Spin3Half), _productionstates(4),
			 _decaystates(4), _currentstates(4), 
			 _decaycalc(false) {}

  /**
   * Standard Constructor.
   * @param p the production momentum.
   * @param time true if the particle is time-like.
   */
  RSFermionSpinInfo(const Lorentz5Momentum & p,bool time)
    : SpinInfo(PDT::Spin3Half, p, time),
      _productionstates(4), _decaystates(4), _currentstates(4), 
      _decaycalc(false) {}
  //@}

public:

  /** @name Set and get methods for the basis state. */
  //@{
  /**
   * Set the basis state, this is production state.
   * @param hel the helicity (0,1,2,3 as described above.)
   * @param in the LorentzRSSpinor for the given helicity.
   */
  void setBasisState(unsigned int hel,
		     const LorentzRSSpinor<SqrtEnergy> & in) const {
    assert(hel<4);
    _productionstates[hel] = in;
    _currentstates   [hel] = in;
  }

  /**
   * Set the basis state for the decay.
   * @param hel the helicity (0,1,2,3 as described above.)
   * @param in the LorentzRSSpinor for the given helicity.
   */
  void setDecayState(unsigned int hel,
		     const LorentzRSSpinor<SqrtEnergy> & in) const {
    assert(hel<4);
    _decaycalc = true;
    _decaystates[hel] = in;
  }

  /**
   * Get the basis state for the production for the given helicity, \a
   * hel (0,1,2,3 as described above.)
   */
  const LorentzRSSpinor<SqrtEnergy> & getProductionBasisState(unsigned int hel) const {
    assert(hel<4);
    return _productionstates[hel];
  }

  /**
   * Get the basis state for the decay for the given helicity, \a hel
   * (0,1,2,3 as described above.)
   */
  const LorentzRSSpinor<SqrtEnergy> & getDecayBasisState(unsigned int hel) const {
    assert(hel<4);
    if(!_decaycalc) {
      for(unsigned int ix=0;ix<4;++ix) _decaystates[ix]=_currentstates[ix];
      _decaycalc=true;
    }
    return _decaystates[hel];
  }

  /**
   * Perform a lorentz rotation of the spin information
   */
  virtual void transform(const LorentzMomentum &,const LorentzRotation &);
  //@}

public:

  /**
   * Standard Init function used to initialize the interfaces.
   */
  static void Init();

  /**
   * Standard clone method.
   */
  virtual EIPtr clone() const;

private:

  /**
   * Describe a concrete class without persistent data.
   */
  static NoPIOClassDescription<RSFermionSpinInfo> initRSFermionSpinInfo;

  /**
   * Private and non-existent assignment operator.
   */
  RSFermionSpinInfo & operator=(const RSFermionSpinInfo &);

private:

  /**
   * Basis states in the frame in which the particle was produced.
   */
  mutable vector<LorentzRSSpinor<SqrtEnergy> > _productionstates;

  /**
   * Basis states in the frame in which the particle decays.
   */
  mutable vector<LorentzRSSpinor<SqrtEnergy> > _decaystates;

  /**
   * Basis states in the current frame of the particle
   */
  mutable vector<LorentzRSSpinor<SqrtEnergy> > _currentstates;

  /**
   * True if the decay state has been set.
   */
  mutable bool _decaycalc;

};

}
}


#include "ThePEG/Utilities/ClassTraits.h"

namespace ThePEG {

/** @cond TRAITSPECIALIZATIONS */

/**
 * The following template specialization informs ThePEG about the
 * base class of RSFermionSpinInfo.
 */
template <>
struct BaseClassTrait<ThePEG::Helicity::RSFermionSpinInfo,1> {
  /** Typedef of the base class of RSFermionSpinInfo. */
  typedef ThePEG::SpinInfo NthBase;
};

/**
 * The following template specialization informs ThePEG about the
 * name of this class and the shared object where it is defined.
 */
template <>
struct ClassTraits<ThePEG::Helicity::RSFermionSpinInfo>
  : public ClassTraitsBase<ThePEG::Helicity::RSFermionSpinInfo> {
  /**
   * Return the class name.
   */
  static string className() { return "ThePEG::Helicity::RSFermionSpinInfo"; }
};

/** @endcond */

}

#endif /* THEPEG_RSFermionSpinInfo_H */