herwig is hosted by Hepforge, IPPP Durham
Herwig  7.1.5
Herwig::ShowerAlpha Class Referenceabstract

This class is the abstract class from which all types of running couplings used in the Showering derive from. More...

#include <ShowerAlpha.h>

Inheritance diagram for Herwig::ShowerAlpha:

Public Member Functions

Standard constructors and destructors.
 ShowerAlpha ()
 The default constructor.
 
virtual double value (const Energy2 scale) const =0
 Methods to return the coupling and the scaleFactor. More...
 
virtual double overestimateValue () const =0
 Virtual method, which should be overridden in a derived class to provide an overestimate approximation of the alpha value.
 
virtual double ratio (const Energy2 scale, double factor=1.) const =0
 Virtual method which returns the ratio of the running alpha value at the input scale to the overestimated value. More...
 
double scaleFactor () const
 It returns the factor that multiplies the scale argument, $\mu^2$, of the running coupling. More...
 
virtual void initialize ()
 Initialize this coupling.
 
Functions used by the persistent I/O system.
void persistentOutput (PersistentOStream &os) const
 Function used to write out object persistently. More...
 
void persistentInput (PersistentIStream &is, int version)
 Function used to read in object persistently. More...
 
- Public Member Functions inherited from ThePEG::Interfaced
virtual bool defaultInit ()
 
PPtr getParticle (PID) const
 
PDPtr getParticleData (PID) const
 
bool used () const
 
void useMe () const
 
tEGPtr generator () const
 
void persistentOutput (PersistentOStream &os) const
 
void persistentInput (PersistentIStream &is, int version)
 
PPtr getParticle (PID) const
 
PDPtr getParticleData (PID) const
 
bool used () const
 
void useMe () const
 
tEGPtr generator () const
 
void persistentOutput (PersistentOStream &os) const
 
void persistentInput (PersistentIStream &is, int version)
 
- Public Member Functions inherited from ThePEG::InterfacedBase
string fullName () const
 
string name () const
 
string path () const
 
string comment () const
 
void setup (istream &is)
 
virtual IBPtr fullclone () const
 
virtual void debugme () const
 
void update ()
 
void init ()
 
virtual bool preInitialize () const
 
void initrun ()
 
void finish ()
 
void touch ()
 
void reset ()
 
void clear ()
 
InitState state () const
 
bool locked () const
 
bool touched () const
 
void persistentOutput (PersistentOStream &os) const
 
void persistentInput (PersistentIStream &is, int version)
 
void update ()
 
void init ()
 
virtual bool preInitialize () const
 
void initrun ()
 
void finish ()
 
void touch ()
 
void reset ()
 
void clear ()
 
InitState state () const
 
bool locked () const
 
bool touched () const
 
void persistentOutput (PersistentOStream &os) const
 
void persistentInput (PersistentIStream &is, int version)
 
- Public Member Functions inherited from ThePEG::Base
void debug () const
 
- Public Member Functions inherited from ThePEG::Pointer::ReferenceCounted
CounterType referenceCount () const
 
- Public Member Functions inherited from ThePEG::Named
 Named (const string &newName=string())
 
const string & name () const
 
bool operator== (const Named &other) const
 
bool operator< (const Named &other) const
 

Static Public Member Functions

static void Init ()
 The standard Init function used to initialize the interfaces. More...
 
- Static Public Member Functions inherited from ThePEG::Interfaced
static void Init ()
 
- Static Public Member Functions inherited from ThePEG::InterfacedBase
static void Init ()
 
- Static Public Member Functions inherited from ThePEG::Base
static void Init ()
 

Private Member Functions

ShowerAlphaoperator= (const ShowerAlpha &)=delete
 The assignment operator is private and must never be called. More...
 

Private Attributes

double _scaleFactor
 The scale factor.
 

Additional Inherited Members

- Public Types inherited from ThePEG::InterfacedBase
enum  InitState
 
- Public Types inherited from ThePEG::Pointer::ReferenceCounted
typedef unsigned int CounterType
 
- Public Attributes inherited from ThePEG::InterfacedBase
 initializing
 
 uninitialized
 
 initialized
 
 runready
 
- Public Attributes inherited from ThePEG::Pointer::ReferenceCounted
const unsigned long uniqueId
 
- Protected Member Functions inherited from ThePEG::Interfaced
void reporeg (IBPtr object, string name) const
 
bool setDefaultReference (PtrT &ptr, string classname, string objectname)
 
 Interfaced (const string &newName)
 
 Interfaced (const Interfaced &i)
 
void setGenerator (tEGPtr generator)
 
- Protected Member Functions inherited from ThePEG::InterfacedBase
virtual IBPtr clone () const=0
 
 InterfacedBase (string newName)
 
 InterfacedBase (const InterfacedBase &i)
 
virtual void readSetup (istream &is)
 
virtual void doupdate ()
 
virtual void doinit ()
 
virtual void doinitrun ()
 
virtual void dofinish ()
 
virtual IVector getReferences ()
 
virtual void rebind (const TranslationMap &)
 
virtual void readSetup (istream &is)
 
virtual void doupdate ()
 
virtual void doinit ()
 
virtual void doinitrun ()
 
virtual void dofinish ()
 
virtual IVector getReferences ()
 
virtual void rebind (const TranslationMap &)
 
- Protected Member Functions inherited from ThePEG::Pointer::ReferenceCounted
 ReferenceCounted (const ReferenceCounted &)
 
ReferenceCountedoperator= (const ReferenceCounted &)
 
 ReferenceCounted (const ReferenceCounted &)
 
ReferenceCountedoperator= (const ReferenceCounted &)
 
- Protected Member Functions inherited from ThePEG::Named
const Namedoperator= (const Named &other)
 
const string & name (const string &newName)
 
- Static Protected Member Functions inherited from ThePEG::Interfaced
static void registerRepository (IBPtr)
 
static void registerRepository (IBPtr, string newName)
 

Detailed Description

This class is the abstract class from which all types of running couplings used in the Showering derive from.

The main purpose of this class, and the ones that derive from it, is to allow systematic uncertainties for the initial-state radiation and, independently, the final-state radiation effects, to be evaluated.

This is achieved by allowing a multiplicative factor, which is 1.0 for the "central value", for the scale argument, $\mu^2$, of the running coupling. This factor, $f$ is given by the scaleFactor() member and the coupling returned by the value() member is such that

\[\alpha(\mu^2)\to \alpha(f\times\mu^2).\]

This scale factor is a parameter which is settable by the user, via the interface. Although, of course, it is not clear my how much we should scale in order to get a $1\sigma$ systematic error (but factors: 1/2 and 2 are quite common), this method provides a double side error, and it appears more sensible than the rough and one-sided evaluation obtained via turning off the I.S.R. and/or F.S.R. (possibilities which are, anyway, provided by Herwig).

See also
The interfaces defined for ShowerAlpha.

Definition at line 49 of file ShowerAlpha.h.

Member Function Documentation

◆ Init()

static void Herwig::ShowerAlpha::Init ( )
static

The standard Init function used to initialize the interfaces.

Called exactly once for each class by the class description system before the main function starts or when this class is dynamically loaded.

◆ operator=()

ShowerAlpha& Herwig::ShowerAlpha::operator= ( const ShowerAlpha )
privatedelete

The assignment operator is private and must never be called.

In fact, it should not even be implemented.

◆ persistentInput()

void Herwig::ShowerAlpha::persistentInput ( PersistentIStream is,
int  version 
)

Function used to read in object persistently.

Parameters
isthe persistent input stream read from.
versionthe version number of the object when written.

◆ persistentOutput()

void Herwig::ShowerAlpha::persistentOutput ( PersistentOStream os) const

Function used to write out object persistently.

Parameters
osthe persistent output stream written to.

◆ ratio()

virtual double Herwig::ShowerAlpha::ratio ( const Energy2  scale,
double  factor = 1. 
) const
pure virtual

Virtual method which returns the ratio of the running alpha value at the input scale to the overestimated value.

Parameters
scaleThe scale
Returns
The ratio

Implemented in Herwig::ShowerAlphaQED, and Herwig::ShowerAlphaQCD.

◆ scaleFactor()

double Herwig::ShowerAlpha::scaleFactor ( ) const
inline

It returns the factor that multiplies the scale argument, $\mu^2$, of the running coupling.

This is supposed to be 1.0 in normal conditions (central values) whereas different values can be useful for systematics evaluation for Initial State radiation or Final State radiation effects.

Definition at line 97 of file ShowerAlpha.h.

◆ value()

virtual double Herwig::ShowerAlpha::value ( const Energy2  scale) const
pure virtual

Methods to return the coupling and the scaleFactor.

Pure virtual method that is supposed to return the running alpha value evaluated at the input scale.

Parameters
scaleThe scale
Returns
The coupling

Implemented in Herwig::ShowerAlphaQED, and Herwig::ShowerAlphaQCD.


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