LHAPDF::AlphaS Class Reference

Calculator interface for computing alpha_s(Q2) in various ways. More...

#include <AlphaS.h>

Inheritance diagram for LHAPDF::AlphaS:

Public Member Functions
	AlphaS ()
	Base class constructor for default param setup.
virtual	~AlphaS ()
	Destructor.
alpha_s values
double	alphasQ (double q) const
	Calculate alphaS(Q)
virtual double	alphasQ2 (double q2) const =0

Protected Member Functions
Calculating beta function values
double	_beta (int i, int nf) const
std::vector< double >	_betas (int nf) const

Protected Attributes
int	_qcdorder
	Order of QCD evolution (expressed as number of loops)
double	_mz
	Mass of the Z boson in GeV.
double	_alphas_mz
	Value of alpha_s(MZ)
double	_mreference
	Reference mass in GeV.
double	_alphas_reference
	Value of alpha_s(reference mass)
bool	_customref
	Decides whether to use custom reference values or fall back on MZ/AlphaS_MZ.
std::map< int, double >	_quarkmasses
std::map< int, double >	_flavorthresholds
FlavorScheme	_flavorscheme
	The flavor scheme in use.
int	_fixflav
	The allowed numbers of flavours in a fixed scheme.

alpha_s metadata
enum	FlavorScheme { FIXED , VARIABLE }
	Enum of flavor schemes.
int	numFlavorsQ (double q) const
	Calculate the number of active flavours at energy scale Q.
virtual int	numFlavorsQ2 (double q2) const
	Calculate the number of active flavours at energy scale Q2.
double	quarkMass (int id) const
	Get a quark mass by PDG code.
void	setQuarkMass (int id, double value)
	Set quark masses by PDG code. More...
double	quarkThreshold (int id) const
	Get a flavor scale threshold by PDG code. More...
void	setQuarkThreshold (int id, double value)
	Set a flavor threshold by PDG code (= quark masses by default) More...
int	orderQCD ()
void	setOrderQCD (int order)
	Set the order of QCD (expressed as number of loops) More...
void	setMZ (double mz)
	Set the Z mass used in this alpha_s. More...
void	setAlphaSMZ (double alphas)
	Set the alpha_s(MZ) used in this alpha_s. More...
void	setMassReference (double mref)
	Set the Z mass used in this alpha_s. More...
void	setAlphaSReference (double alphas)
	Set the alpha_s(MZ) used in this alpha_s. More...
virtual void	setLambda (unsigned int, double)
	Set the {i}th Lambda constant for i active flavors. More...
virtual std::string	type () const =0
	Get the implementation type of this AlphaS.
void	setFlavorScheme (FlavorScheme scheme, int nf=-1)
	Set flavor scheme of alpha_s solver.
FlavorScheme	flavorScheme () const
	Get flavor scheme.

Detailed Description

Calculator interface for computing alpha_s(Q2) in various ways.

The design of the AlphaS classes is that they are substitutible (cf. polymorphism) and are entirely non-dependent on the PDF and Info objects: hence they can be used by external code that actually doesn't want to do anything at all with PDFs, but which just wants to do some alpha_s interpolation.

Member Function Documentation

_beta()

double LHAPDF::AlphaS::_beta ( int  i, int  nf  ) const

protected

Calculate the i'th beta function given the number of active flavours Currently limited to 0 <= i <= 3 Calculated using the MSbar scheme

_betas()

std::vector<double> LHAPDF::AlphaS::_betas ( int  nf ) const

protected

Calculate a vector of beta functions given the number of active flavours Currently returns a 4-element vector of beta0 – beta3

alphasQ2()

virtual double LHAPDF::AlphaS::alphasQ2 ( double  q2 ) const

pure virtual

Calculate alphaS(Q2)

Todo:

Throw error in this base method if Q < Lambda?

Implemented in LHAPDF::AlphaS_ODE, LHAPDF::AlphaS_Ipol, and LHAPDF::AlphaS_Analytic.

orderQCD()

int LHAPDF::AlphaS::orderQCD ( )

inline

Get the order of QCD (expressed as number of loops)

Used explicitly in the analytic and ODE solvers.

quarkThreshold()

double LHAPDF::AlphaS::quarkThreshold

(

int

id

)

const

Get a flavor scale threshold by PDG code.

Used in the analytic and ODE solvers.

setAlphaSMZ()

void LHAPDF::AlphaS::setAlphaSMZ ( double  alphas )

inline

Set the alpha_s(MZ) used in this alpha_s.

Used in the ODE solver.

setAlphaSReference()

void LHAPDF::AlphaS::setAlphaSReference ( double  alphas )

inline

Set the alpha_s(MZ) used in this alpha_s.

Used in the ODE solver.

setLambda()

virtual void LHAPDF::AlphaS::setLambda ( unsigned int  , double    )

inlinevirtual

Set the {i}th Lambda constant for i active flavors.

Used in the analytic solver.

Reimplemented in LHAPDF::AlphaS_Analytic.

setMassReference()

void LHAPDF::AlphaS::setMassReference ( double  mref )

inline

Set the Z mass used in this alpha_s.

Used in the ODE solver.

setMZ()

void LHAPDF::AlphaS::setMZ ( double  mz )

inline

Set the Z mass used in this alpha_s.

Used in the ODE solver.

setOrderQCD()

void LHAPDF::AlphaS::setOrderQCD ( int  order )

inline

Set the order of QCD (expressed as number of loops)

Used in the analytic and ODE solvers.

setQuarkMass()

void LHAPDF::AlphaS::setQuarkMass	(	int	id,
		double	value
	)

Set quark masses by PDG code.

Used in the analytic and ODE solvers.

setQuarkThreshold()

void LHAPDF::AlphaS::setQuarkThreshold	(	int	id,
		double	value
	)

Set a flavor threshold by PDG code (= quark masses by default)

Used in the analytic and ODE solvers.

Member Data Documentation

_quarkmasses

std::map<int, double> LHAPDF::AlphaS::_quarkmasses

protected

Masses of quarks in GeV Used for working out flavor thresholds and the number of quarks that are active at energy scale Q.

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The documentation for this class was generated from the following file:

• /builds/hepcedar/lhapdf/include/LHAPDF/AlphaS.h