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//==============================================================================
// AlphaStrong.h
//
// Copyright (C) 2010-2013 Tobias Toll and Thomas Ullrich
//
// This file is part of Sartre version: 1.1
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation.
// This program is distributed in the hope that it will be useful,
// but without any warranty; without even the implied warranty of
// merchantability or fitness for a particular purpose. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//
// Author: Thomas Ullrich
// Last update:
// $Date: 2013-05-29 21:26:19 +0100 (Wed, 29 May 2013) $
// $Author: thomas.ullrich@bnl.gov $
//==============================================================================
//
// Original code from Pythia8:
// Copyright (C) 2010 Torbjorn Sjostrand.
// PYTHIA is licenced under the GNU GPL version 2, see COPYING for details.
//
// The code was modified for Sartre and made multithread safe and several
// methods that are not needed in Sartre were removed.
// The formula this code is based on is from:
// Particle Data Group, W.-M. Yao et al., J. Phys. G33 (2006) 1
//
// Notes on alpha_s values at M_Z:
// In the MRST alpha_s code the following values are used:
// LO: 0.13939
// NLO: 0.12018
// NNLO: 0.11707
//
// PDG (2011) quotes: 0.1184
//
// Pythia uses values varying from 0.12-0.13939 depending on where it is used.
//
// This version with order=1 is identical to MRST LO,
// order=2 is close to MRST NLO for Q>2 GeV. order=0 is constant.
//==============================================================================
#ifndef AlphaStrong_h
#define AlphaStrong_h
class AlphaStrong {
public:
AlphaStrong(double alphasAtMZ = 0.12, int order = 1);
void init(double alphasAtMZ, int order);
double alphaS(double Q2); // Q2 is the Q^2 scale in GeV^2
private:
double pow2(double) const;
private:
static const int mMaxIter = 10;
static const double mMassC;
static const double mMassB;
static const double mMassZ;
static const double mSafetyMargin1;
static const double mSafetyMargin2;
private:
bool mIsInit;
int mOrder;
double mValueRef;
double mValueNow, mScale2Now, mScale2Min;
double mMassC2, mMassB2;
double mLambda3Save, mLambda4Save, mLambda5Save;
double mLambda3Save2, mLambda4Save2, mLambda5Save2;
};
inline double AlphaStrong::pow2(double x) const {return x*x;}
#endif

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