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 ThePEG  2.1.5
ThePEG::SimplePhaseSpace Namespace Reference

SimplePhaseSpace defines a set of static functions to be used for distributing momenta evenly in phase space. More...

## Functions

template<typename PType >
void CMS (Energy2 s, PType &p1, PType &p2)
Set two momenta in their center of mass system. More...

template<typename PType >
void CMS (PType &p1, PType &p2, Energy2 s, double cosTheta, double phi)
Set two momenta in their center of mass system. More...

template<typename PType >
void CMS (PType &p1, PType &p2, Energy2 s, Energy2 t, double phi, const PType &p0)
Set two momenta in their center of mass system. More...

template<typename PType >
void CMS (PType &p1, PType &p2, Energy2 s)
Set two momenta in their center of mass system. More...

template<typename PPairType >
void CMS (const PPairType &p, Energy2 s)
Set two momenta in their center of mass system. More...

template<typename PType >
void CMS (PType &p1, PType &p2, PType &p3, Energy2 s, double x1, double x3)
Set three momenta in their center of mass system. More...

template<typename PType >
void CMS (PType &p1, PType &p2, PType &p3, Energy2 s, double x1, double x3, double phii=0.0, double theta=0.0, double phi=0.0)
Set three momenta in their center of mass system. More...

Energy getMagnitude (Energy2 s, Energy m1, Energy m2)
Calculate the absolute magnitude of the momenta of two particles with masses m1 and m2 when put in their CMS of total invariant mass squared s. More...

Momentum3 polar3Vector (Energy p, double costheta, double phi)
Return a three-vector given the absolute momentum, cos(theta) and phi. More...

vector< LorentzMomentumCMSn (Energy m0, const vector< Energy > &m)
Get a number of randomly distributed momenta. More...

template<typename Container >
void CMSn (Container &particles, Energy m0)
Set the momentum of a number of particles. More...

## Detailed Description

SimplePhaseSpace defines a set of static functions to be used for distributing momenta evenly in phase space.

In most cases pointers and references to both particle and momentum objects can be used as arguments as long as the ParticleTraits class is specialized properly. When needed, random numbers are generated with the generator given by the static UseRandom class.

## ◆ CMS() [1/7]

template<typename PType >
 void ThePEG::SimplePhaseSpace::CMS ( Energy2 s, PType & p1, PType & p2 )

Set two momenta in their center of mass system.

Their total invariant mass squared is given by s, and their direction is distributed isotropically.

Parameters
 s the total invariant mass squared. p1 pointer or reference to the first momentum. Its invariant mass will be preserved. p2 pointer or reference to the second momentum. Its invariant mass will be preserved.
Exceptions
 ImpossibleKinematics if the sum of the invariant masses was larger than the given invariant mass ( ).

Referenced by CMS().

## ◆ CMS() [2/7]

template<typename PType >
 void ThePEG::SimplePhaseSpace::CMS ( PType & p1, PType & p2, Energy2 s, double cosTheta, double phi )

Set two momenta in their center of mass system.

Their total invariant mass squared is given by s, and their direction is given in terms of the polar and azimuth angle of the first momenta.

Parameters
 s the total invariant mass squared. p1 pointer or reference to the first momentum. Its invariant mass will be preserved. p2 pointer or reference to the second momentum. Its invariant mass will be preserved. cosTheta cosine of the azimuth angle of the first momentum. phi azimuth angle of the first momentum.
Exceptions
 ImpossibleKinematics if the sum of the invariant masses was larger than the given invariant mass ( ).

## ◆ CMS() [3/7]

template<typename PType >
 void ThePEG::SimplePhaseSpace::CMS ( PType & p1, PType & p2, Energy2 s, Energy2 t, double phi, const PType & p0 )

Set two momenta in their center of mass system.

Their total invariant mass squared is given by s. The helper momentum p0 is used so that afterwards and p1 has the azimuth angle phi around p0.

Parameters
 p1 pointer or reference to the first momentum. Its invariant mass will be preserved. p2 pointer or reference to the second momentum. Its invariant mass will be preserved. s the total invariant mass squared. t . phi azimuth angle of the first momentum around p0. p0 pointer or reference to an auxiliary momentum.
Exceptions
 ImpossibleKinematics if the sum of the invariant masses was larger than the given invariant mass ( ).

## ◆ CMS() [4/7]

template<typename PType >
 void ThePEG::SimplePhaseSpace::CMS ( PType & p1, PType & p2, Energy2 s )

Set two momenta in their center of mass system.

Their total invariant mass squared is given by s. p1 will be along the z-axis.

Parameters
 p1 pointer or reference to the first momentum. Its invariant mass will be preserved. p2 pointer or reference to the second momentum. Its invariant mass will be preserved. s the total invariant mass squared.
Exceptions
 ImpossibleKinematics if the sum of the invariant masses was larger than the given invariant mass ( ).

## ◆ CMS() [5/7]

template<typename PPairType >
 void ThePEG::SimplePhaseSpace::CMS ( const PPairType & p, Energy2 s )

Set two momenta in their center of mass system.

Their total invariant mass squared is given by s. The first will be along the z-axis.

Parameters
 p a pair of pointers or references to the two momenta. Their invariant masses will be preserved. s the total invariant mass squared.
Exceptions
 ImpossibleKinematics if the sum of the invariant masses was larger than the given invariant mass ( ).

Definition at line 113 of file SimplePhaseSpace.h.

References CMS(), and getMagnitude().

## ◆ CMS() [6/7]

template<typename PType >
 void ThePEG::SimplePhaseSpace::CMS ( PType & p1, PType & p2, PType & p3, Energy2 s, double x1, double x3 )

Set three momenta in their center of mass system.

Their total invariant mass squared is given by s. The energy fraction of particle p1(3) is x1(3) of the total energy and the angles of the system is distributed isotropically.

Parameters
 p1 pointer or reference to the first momentum. Its invariant mass will be preserved. p2 pointer or reference to the second momentum. Its invariant mass will be preserved. p3 pointer or reference to the second momentum. Its invariant mass will be preserved. s the total invariant mass squared. x1 the energy fraction . x3 the energy fraction .
Exceptions
 ImpossibleKinematics if the sum of the invariant masses was larger than the given invariant mass ( ).

## ◆ CMS() [7/7]

template<typename PType >
 void ThePEG::SimplePhaseSpace::CMS ( PType & p1, PType & p2, PType & p3, Energy2 s, double x1, double x3, double phii = 0.0, double theta = 0.0, double phi = 0.0 )

Set three momenta in their center of mass system.

Their total invariant mass squared is given by s. The energy fraction of particle p1(3) is x1(3) of the total energy. Particle p1 is initially placed along the z-axis and particle p2 is given azimuth angle phii. Then the system is then rotated with theta and phi respectively.

Parameters
 p1 pointer or reference to the first momentum. Its invariant mass will be preserved. p2 pointer or reference to the second momentum. Its invariant mass will be preserved. p3 pointer or reference to the second momentum. Its invariant mass will be preserved. s the total invariant mass squared. x1 the energy fraction . x3 the energy fraction . phii the azimuth angle of p2 around p1. theta the polar angle of p1. phi the azimuth angle of p1.
Exceptions
 ImpossibleKinematics if the sum of the invariant masses was larger than the given invariant mass ( ).

## ◆ CMSn() [1/2]

 vector ThePEG::SimplePhaseSpace::CMSn ( Energy m0, const vector< Energy > & m )

Get a number of randomly distributed momenta.

Given a number specified invariant masses and a total invariant mass m0, return corresponding four-momenta randomly distributed according to phase space.

Parameters
 m0 the total invariant mass of the resulting momenta. m a vector of invariant masses of the resulting momenta.
Returns
a vector of momenta with the given masses randomly distributed.
Exceptions
 ImpossibleKinematics if the sum of the masses was larger than the given invariant mass ( ).

Referenced by polar3Vector().

## ◆ CMSn() [2/2]

template<typename Container >
 void ThePEG::SimplePhaseSpace::CMSn ( Container & particles, Energy m0 )

Set the momentum of a number of particles.

Given a number of particles and a total invariant mass m0, distribute their four-momenta randomly according to phase space.

Parameters
 particles a container of particles or pointers to particles. The invariant mass of these particles will not be chaned. m0 the total invariant mass of the resulting momenta.
Exceptions
 ImpossibleKinematics if the sum of the masses was larger than the given invariant mass ( ).

## ◆ getMagnitude()

 Energy ThePEG::SimplePhaseSpace::getMagnitude ( Energy2 s, Energy m1, Energy m2 )

Calculate the absolute magnitude of the momenta of two particles with masses m1 and m2 when put in their CMS of total invariant mass squared s.

Parameters
 s the total invariant mass squared. m1 the mass of particle 1. m2 the mass of particle 2.
Exceptions
 ImpossibleKinematics if the sum of the masses was larger than the given invariant mass ( ).

Referenced by CMS().

## ◆ polar3Vector()

 Momentum3 ThePEG::SimplePhaseSpace::polar3Vector ( Energy p, double costheta, double phi )
inline

Return a three-vector given the absolute momentum, cos(theta) and phi.

Parameters
 p the magnitude of the momentum. costheta the cosine of the polar angle. phi the azimuth angle.

Definition at line 185 of file SimplePhaseSpace.h.

References CMSn().