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PYTHIA
8.316
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#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, double valueMaxIn=-1., double renormShiftIn=0.) |
| 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... | |
| double | alphaSmax () |
| Return the alphaSmax value. | |
| double | renormShift () |
| Return the poleShift value. | |
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 |
The AlphaStrong class calculates the alpha_strong value at an arbitrary scale, given the value at m_Z, to first, second or third order.
| double alphaS | ( | double | scale2 | ) |
alpha_S value and Lambda values.
Calculate alpha_s value.
Check for initialization and ensure minimal scale2 value.
Optionally shift argument to avoid pole.
Freeze below minimum scale.
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/third order alpha_s: differs by mass region.
Done.
| double alphaS2OrdCorr | ( | double | scale2 | ) |
Calculates the second- or third-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.
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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 or third order alpha_s: iterative match at flavour thresholds.
The two-loop coefficients: b1 / b0^2
The three-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.
Maximum return value (to freeze effective coupling at max value). Negative values => do not impose any specific uppper bound.
Optionally shift renormalisation scale2 -> scale2 + x * Lambda3^2. A value of x = 1 shifts the pole to input scale 0. Values greater than 1 produce finite alphaS values at zero input scale. Changes for perturbative input scales (>> Lambda3) are small since the input scale is only shifted by O(Lambda3).
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).
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protected |
Protected data members: accessible to derived classes.
Initialization data member.
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staticprotected |
Flavour thresholds.
MZ normalization scale.
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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.
1.8.11
