StandardModel.h

// StandardModel.h is a part of the PYTHIA event generator.
// Copyright (C) 2011 Torbjorn Sjostrand.
// PYTHIA is licenced under the GNU GPL version 2, see COPYING for details.
// Please respect the MCnet Guidelines, see GUIDELINES for details.

// This file gives access to some Standard Model parameters.
// AlphaStrong: fix or first- or second-order running alpha_strong.

#ifndef StandardModel_H
#define StandardModel_H


//==========================================================================

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

class AlphaStrong {

public:

  // Constructors.
  AlphaStrong() : isInit(false) {}
  AlphaStrong(double valueIn, int orderIn = 1) { 
    init( valueIn, orderIn) ;}

  // Initialization for given value at M_Z and given order.
  void init(double valueIn = 0.12, int orderIn = 1);

  // alpha_S value and Lambda values.
  double alphaS(double scale2) const;
  double alphaS1Ord(double scale2);
  double alphaS2OrdCorr(double scale2);
  double Lambda3() const { return Lambda3Save; }
  double Lambda4() const { return Lambda4Save; }
  double Lambda5() const { return Lambda5Save; }

protected:

  // Initialization data member; protected to allow inheritance.
  bool   isInit;

private:

  // Constants: could only be changed in the code itself.
  static const int    NITER;
  static const double MC, MB, MZ, SAFETYMARGIN1, SAFETYMARGIN2;

  // Data members.
  mutable bool   lastCallToFull;
  int    order;
  double valueRef, scale2Min, Lambda3Save, 
         Lambda4Save, Lambda5Save, Lambda3Save2, Lambda4Save2, 
         Lambda5Save2, mc, mb, mZ, mc2, mb2;
  mutable double scale2Now, valueNow;

};



#endif // Pythia8_StandardModel_H