PYTHIA  8.303
Public Member Functions | Protected Attributes | Static Protected Attributes | List of all members
AlphaStrong Class Reference

#include <StandardModel.h>

Public Member Functions

 AlphaStrong ()
 Constructors.
 
virtual ~AlphaStrong ()
 Destructor.
 
virtual void init (double valueIn=0.12, int orderIn=1, int nfmaxIn=6, bool useCMWIn=false)
 Initialization for given value at M_Z and given order. More...
 
virtual void setThresholds (double mcIn, double mbIn, double mtIn)
 Set flavour threshold values: m_c, m_b, m_t.
 
double alphaS (double scale2)
 alpha_S value and Lambda values. More...
 
double alphaS1Ord (double scale2)
 
double alphaS2OrdCorr (double scale2)
 
double Lambda3 () const
 
double Lambda4 () const
 
double Lambda5 () const
 
double Lambda6 () const
 
double muThres (int idQ)
 Info: tell which scales we use for flavour thresholds. More...
 
double muThres2 (int idQ)
 
double facCMW (int nFin)
 Return the CMW factor (for nF between 3 and 6). More...
 

Protected Attributes

bool isInit
 Protected data members: accessible to derived classes. More...
 
int order
 Running order and max number of flavours to use in running.
 
int nfmax
 
double Lambda3Save
 Lambda values.
 
double Lambda4Save
 
double Lambda5Save
 
double Lambda6Save
 
double Lambda3Save2
 
double Lambda4Save2
 
double Lambda5Save2
 
double Lambda6Save2
 
double scale2Min
 Smallest allowed renormalization scale.
 
double mc
 
double mb
 
double mt
 
double mc2
 
double mb2
 
double mt2
 
bool useCMW
 CMW rescaling factors.
 

Static Protected Attributes

static const double MZ = 91.188
 Flavour thresholds. More...
 
static const double FACCMW3 = 1.661
 CMW factor for 3, 4, 5, and 6 flavours.
 
static const double FACCMW4 = 1.618
 
static const double FACCMW5 = 1.569
 
static const double FACCMW6 = 1.513
 
static const double SAFETYMARGIN1 = 1.07
 Safety margins to avoid getting too close to LambdaQCD. More...
 
static const double SAFETYMARGIN2 = 1.33
 

Detailed Description

The AlphaStrong class calculates the alpha_strong value at an arbitrary scale, given the value at m_Z, to zeroth, first or second order.

Member Function Documentation

double alphaS ( double  scale2)

alpha_S value and Lambda values.

Calculate alpha_s value.

Check for initialization and ensure minimal scale2 value.

If equal to old scale then same answer.

Fix alpha_s.

First order alpha_s: differs by mass region.

Second order alpha_s: differs by mass region.

Done.

double alphaS1Ord ( double  scale2)

Calculate alpha_s value, but only use up to first-order piece. (To be combined with alphaS2OrdCorr.)

Check for initialization and ensure minimal scale2 value.

If equal to old scale then same answer.

Fix alpha_S.

First/second order alpha_s: differs by mass region.

Done.

double alphaS2OrdCorr ( double  scale2)

Calculates the second-order extra factor in alpha_s. (To be combined with alphaS1Ord.)

Check for initialization and ensure minimal scale2 value.

Only meaningful for second-order calculations.

Second order correction term: differs by mass region.

double facCMW ( int  nFin)

Return the CMW factor (for nF between 3 and 6).

facCMW: tells what values of the CMW factors are being used (if any).

Return unity if we are not doing CMW rescaling..

Else return the NF-dependent value of the CMW rescaling factor.

void init ( double  valueIn = 0.12,
int  orderIn = 1,
int  nfmaxIn = 6,
bool  useCMWIn = false 
)
virtual

Initialization for given value at M_Z and given order.

Initialize alpha_strong calculation by finding Lambda values etc.

Set default mass thresholds if not already done

Order of alpha_s evaluation.Default values.

Fix alpha_s.

First order alpha_s: match at flavour thresholds.

Second order alpha_s: iterative match at flavour thresholds.

The one-loop coefficients: b1 / b0^2

The two-loop coefficients: b2 * b0 / b1^2

Find Lambda_5 at m_Z, starting from one-loop value

Find Lambda_6 at m_t, by requiring alphaS(nF=6,m_t) = alphaS(nF=5,m_t)

Find Lambda_4 at m_b, by requiring alphaS(nF=4,m_b) = alphaS(nF=5,m_b)

Find Lambda_3 at m_c, by requiring alphaS(nF=3,m_c) = alphaS(nF=4,m_c)

Optionally rescale Lambda values by CMW factor.

Impose SAFETYMARGINs to prevent getting too close to LambdaQCD.

Save squares of mass and Lambda values as well.

double muThres ( int  idQ)

Info: tell which scales we use for flavour thresholds.

muThres(2): tell what values of flavour thresholds are being used.

Return the scale of each flavour threshold included in running.

Else return -1 (indicates no such threshold is included in running).

double muThres2 ( int  idQ)

Return the scale of each flavour threshold included in running.

Else return -1 (indicates no such threshold is included in running).

Member Data Documentation

bool isInit
protected

Protected data members: accessible to derived classes.

Initialization data member.

const double MZ = 91.188
staticprotected

Flavour thresholds.

MZ normalization scale.

const double SAFETYMARGIN1 = 1.07
staticprotected

Safety margins to avoid getting too close to LambdaQCD.

Always evaluate running alpha_s above Lambda3 to avoid disaster. Safety margin picked to freeze roughly for alpha_s = 10.


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