FFBtoDstarCLN.cc

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///
/// @file  FFBtoDstarCLN.cc
/// @brief \f$ B \rightarrow D^* \f$ CLN form factors
/// @brief Ported from EvtGen HQET2
///

//**** This file is a part of the HAMMER library
//**** Copyright (C) 2016 - 2020 The HAMMER Collaboration
//**** HAMMER is licensed under version 3 of the GPL; see COPYING for details
//**** Please note the MCnet academic guidelines; see GUIDELINES for details

// -*- C++ -*-
#include "Hammer/FormFactors/FFBtoDstarCLN.hh"
#include "Hammer/IndexLabels.hh"
#include "Hammer/Math/Constants.hh"
#include "Hammer/Math/Utils.hh"
#include "Hammer/Particle.hh"
#include "Hammer/Tools/Pdg.hh"
#include "Hammer/Math/MultiDim/SparseContainer.hh"
#include <cmath>
#include <iostream>

using namespace std;

namespace Hammer {

    namespace MD = MultiDimensional;

    FFBtoDstarCLN::FFBtoDstarCLN() {
        // Create tensor rank and dimensions
        vector<IndexType> dims = {8};
        string name{"FFBtoDstarCLN"};
        
        setPrefix("BtoD*");
        addProcessSignature(PID::BPLUS, {-PID::DSTAR});
        addTensor(Tensor{name, MD::makeEmptySparse(dims, {FF_BDSTAR})});

        addProcessSignature(PID::BZERO, {PID::DSTARMINUS});
        addTensor(Tensor{name, MD::makeEmptySparse(dims, {FF_BDSTAR})});
        
        setPrefix("BstoDs*");
        addProcessSignature(PID::BS, {PID::DSSTARMINUS});
        addTensor(Tensor{name, MD::makeEmptySparse(dims, {FF_BSDSSTAR})});

        setSignatureIndex();
    }

    void FFBtoDstarCLN::defineSettings() {
        //_FFErrNames = ;
        setPath(getFFErrPrefixGroup().get());
        setUnits("GeV");

        addSetting<double>("a",1.0); //zero recoil expansion
        addSetting<double>("RhoSq",1.207);
        addSetting<double>("F1",0.908);
        addSetting<double>("R1",1.401);
        addSetting<double>("R2",0.854);
        addSetting<double>("R0",1.15);
        addSetting<double>("as",0.26); //mbmc scale
        addSetting<double>("la",0.48); //CLN
        addSetting<double>("mcOnmb",0.29); //CLN
        initialized = true;
    }

    void FFBtoDstarCLN::evalAtPSPoint(const vector<double>& point, const vector<double>& masses) {
        Tensor& result = getTensor();
        result.clearData();

        if(!initialized){
            MSG_WARNING("Warning, Setting have not been defined!");
        }

        double Mb = 0.;
        double Mc = 0.;
        double unitres = 1.;
        if(masses.size() >= 2) {
            Mb = masses[0];
            Mc = masses[1];
            unitres = _units;
        }
        else {
            Mb = this->masses()[0];
            Mc = this->masses()[1];
        }
        const double Mb2 = Mb*Mb;
        const double Mc2 = Mc*Mc;

        double Sqq = point[0];

        // const double sqMbMc = sqrt(Mb*Mc);
        double w = (Mb2 + Mc2 - Sqq)/(2.*Mb*Mc);
        //safety measure if w==1.0
        if(isZero(w - 1.0)) w += 1e-6;
        const double a = *getSetting<double>("a");
        const double zCon = (sqrt(w+1) - sqrt2*a)/(sqrt(w+1) + sqrt2*a);

        const double RhoSq=*getSetting<double>("RhoSq");
        const double R0par=*getSetting<double>("R0");
        const double R1par=*getSetting<double>("R1");
        const double R2par=*getSetting<double>("R2");
        const double F1par=*getSetting<double>("F1");
        const double as = *getSetting<double>("as")/pi;
        const double LambdaBar = *getSetting<double>("la");
        const double zR = *getSetting<double>("mcOnmb");

        const double rC=Mc/Mb;
        const double rC2 = rC*rC;

        //MSbar masses
        const double mbMu = Mb - unitres*LambdaBar - Mb*as*(4./3. + log(zR));
        const double mcMu = Mc - unitres*LambdaBar - Mc*as*(4./3. - log(zR));

        //define the variables
        const double Ha1= F1par*(1. - 8.* RhoSq * zCon +
                                 (53. * RhoSq - 15.) * pow(zCon, 2.)
                                 - (231. * RhoSq - 91.) * pow(zCon, 3.));
        const double R0 = R0par - 0.11 * (w - 1.) + 0.01 * pow(w - 1., 2.);
        const double R1 = R1par - 0.12 * (w - 1.) + 0.05 * pow(w - 1., 2.);
        const double R2 = R2par + 0.11 * (w - 1.) - 0.06 * pow(w - 1., 2.);

        const double Ff = (Ha1*(Mb2*pow(1 + rC,2) - Sqq))/(2.*Mb*sqrt(rC));
        const double Fg = (Ha1*R1)/(2.*Mb*sqrt(rC));
        const double Fm = -(Ha1*(R2*(-1 + rC2) - 2*rC*(-1 + R0 + R0*rC - w)))/(2.*Mb*sqrt(rC)*(1 + rC2 - 2*rC*w));
        const double Fp = -(Ha1*R2)/(2.*Mb*sqrt(rC));
        //Pseudoscalar check!
        const double Fps = -(Ff + Mb2*(Fp*(1-rC2) + Fm*(1 + rC2 - 2*rC*w)))/(mbMu + mcMu);

        // set elements, mapping to amplitude FF basis
        // Fps
        result.element({0}) = Fps;
        // Ff
        result.element({1}) = Ff;
        // Fg
        result.element({2}) = Fg;
        // Fm
        result.element({3}) = Fm;
        // Fp
        result.element({4}) = Fp;
        // Fzt
        // result.element({5}) = 0;
        // Fmt
        // result.element({6}) = 0;
        // Fpt
        // result.element({7}) = 0;

    }

    std::unique_ptr<FormFactorBase> FFBtoDstarCLN::clone(const std::string& label) {
        MAKE_CLONE(FFBtoDstarCLN, label);
    }

} // namespace Hammer