LauLASSRes.cc

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// Copyright University of Warwick 2004 - 2014.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

// Authors:
// Thomas Latham
// John Back
// Paul Harrison

#include <iostream>

#include "LauConstants.hh"
#include "LauLASSRes.hh"
#include "LauResonanceInfo.hh"

ClassImp(LauLASSRes)


LauLASSRes::LauLASSRes(LauResonanceInfo* resInfo, const Int_t resPairAmpInt, const LauDaughters* daughters) :
        LauAbsResonance(resInfo, resPairAmpInt, daughters),
        q0_(0.0),
        mDaugSum_(0.0),
        mDaugSumSq_(0.0),
        mDaugDiff_(0.0),
        mDaugDiffSq_(0.0),
        resMassSq_(0.0),
        r_(0),
        a_(0),
        cutOff_(0.0)
{
        // Default values for LASS parameters
        cutOff_ = 1.8;
        const Double_t rVal = 3.32;
        const Double_t aVal = 2.07;

        const TString& parNameBase = this->getSanitisedName();

        TString rName(parNameBase);
        rName += "_r";
        r_ = resInfo->getExtraParameter( rName );
        if ( r_ == 0 ) {
                r_ = new LauParameter( rName, rVal, 0.0, 10.0, kTRUE );
                r_->secondStage(kTRUE);
                resInfo->addExtraParameter( r_ );
        }

        TString aName(parNameBase);
        aName += "_a";
        a_ = resInfo->getExtraParameter( aName );
        if ( a_ == 0 ) {
                a_ = new LauParameter( aName, aVal, 0.0, 10.0, kTRUE );
                a_->secondStage(kTRUE);
                resInfo->addExtraParameter( a_ );
        }
}

LauLASSRes::~LauLASSRes()
{
}

void LauLASSRes::initialise()
{
        // Create the mass sums and differences
        Double_t massDaug1 = this->getMassDaug1();
        Double_t massDaug2 = this->getMassDaug2();

        mDaugSum_  = massDaug1 + massDaug2;
        mDaugSumSq_ = mDaugSum_*mDaugSum_;

        mDaugDiff_ = massDaug1 - massDaug2;
        mDaugDiffSq_ = mDaugDiff_*mDaugDiff_;

        Int_t resSpin = this->getSpin();
        if (resSpin != 0) {
                std::cerr << "WARNING in LauLASSRes::amplitude : Resonance spin is " << resSpin << "." << std::endl;
                std::cerr << "                                 : LASS amplitude is only for scalers, resetting spin to 0." << std::endl;
                this->changeResonance( -1.0, -1.0, 0 );
        }

        this->calcQ0();
}

void LauLASSRes::calcQ0()
{
        // Decay momentum of either daughter in the resonance rest frame
        // when resonance mass = rest-mass value, m_0 (PDG value)

        resMass_ = this->getMass();
        resMassSq_ = resMass_*resMass_;

        q0_ = TMath::Sqrt((resMassSq_ - mDaugSumSq_)*(resMassSq_ - mDaugDiffSq_))/(2.0*resMass_);
}

LauComplex LauLASSRes::resAmp(Double_t mass, Double_t /*spinTerm*/)
{
        LauComplex resAmplitude(0.0, 0.0);
        LauComplex bkgAmplitude(0.0, 0.0);
        LauComplex totAmplitude(0.0, 0.0);

        if (mass < 1e-10) {
                std::cerr << "WARNING in LauLASSRes::amplitude : mass < 1e-10." << std::endl;
                return LauComplex(0.0, 0.0);
        }

        //---------------------------
        // First do the resonant part
        //---------------------------

        // Calculate the width of the resonance (as a function of mass)
        // q is the momentum of either daughter in the resonance rest-frame
        const Double_t q = this->getQ();
        const Double_t resMass = this->getMass();
        const Double_t resWidth = this->getWidth();

        // If the mass is floating and their value have changed
        // we need to recalculate everything that assumes this value
        if ( (!this->fixMass()) && resMass != resMass_ ) {
                this->calcQ0();
        }

        Double_t qRatio = q/q0_;
        Double_t totWidth = resWidth*qRatio*(resMass/mass);

        Double_t massSq = mass*mass;
        Double_t massSqTerm = resMassSq_ - massSq;

        // Compute the complex amplitude
        resAmplitude = LauComplex(massSqTerm, resMass*totWidth);

        // Scale by the denominator factor
        resAmplitude.rescale((resMassSq_*resWidth/q0_)/(massSqTerm*massSqTerm + resMassSq_*totWidth*totWidth));

        // Calculate the phase shift term
        const Double_t rVal = this->getEffectiveRange();
        const Double_t aVal = this->getScatteringLength();
        const Double_t tandeltaB = (2.0*aVal*q)/(2.0 + aVal*rVal*q*q);
        const Double_t tanSq = tandeltaB*tandeltaB;
        const Double_t cos2PhaseShift = (1.0 - tanSq) / (1.0 + tanSq);
        const Double_t sin2PhaseShift = 2.0*tandeltaB / (1.0 + tanSq);
        LauComplex phaseShift(cos2PhaseShift, sin2PhaseShift);

        // Multiply by the phase shift
        resAmplitude = resAmplitude * phaseShift;


        //--------------------------------
        // Now do the effective range part
        //--------------------------------

        // Form the real and imaginary parts
        const Double_t qcotdeltaB = 1.0/aVal + (rVal*q*q)/2.0;

        // Compute the complex amplitude
        bkgAmplitude = LauComplex(qcotdeltaB, q);

        // Scale by the numerator and denominator factors
        bkgAmplitude.rescale(mass/(qcotdeltaB*qcotdeltaB + q*q));


        //------------------
        // Add them together
        //------------------

        if (mass > cutOff_) {
                totAmplitude = resAmplitude;
        } else {
                totAmplitude = bkgAmplitude + resAmplitude;
        }

        return totAmplitude;
}

const std::vector<LauParameter*>& LauLASSRes::getFloatingParameters()
{
        this->clearFloatingParameters();

        if ( ! this->fixMass() ) {
                this->addFloatingParameter( this->getMassPar() );
        }

        if ( ! this->fixWidth() ) {
                this->addFloatingParameter( this->getWidthPar() );
        }

        if ( ! this->fixEffectiveRange() ) {
                this->addFloatingParameter( r_ );
        }

        if ( ! this->fixScatteringLength() ) {
                this->addFloatingParameter( a_ );
        }

        return this->getParameters();
}

void LauLASSRes::setResonanceParameter(const TString& name, const Double_t value)
{
        // Set various parameters for the LASS lineshape dynamics
        if (name == "a") {
                this->setScatteringLength(value);
                std::cout << "INFO in LauLASSRes::setResonanceParameter : Setting LASS Scattering Length = " << this->getScatteringLength() << std::endl;
        } else if (name == "r") {
                this->setEffectiveRange(value);
                std::cout << "INFO in LauLASSRes::setResonanceParameter : Setting LASS Effective Range = " << this->getEffectiveRange() << std::endl;
        } else {
                std::cerr << "WARNING in LauLASSRes::setResonanceParameter: Parameter name not reconised.  No parameter changes made." << std::endl;
        }
}

void LauLASSRes::floatResonanceParameter(const TString& name)
{
        if (name == "a") {
                if ( a_->fixed() ) {
                        a_->fixed( kFALSE );
                        this->addFloatingParameter( a_ );
                } else {
                        std::cerr << "WARNING in LauLASSRes::floatResonanceParameter: Parameter already floating.  No parameter changes made." << std::endl;
                }
        } else if (name == "r") {
                if ( r_->fixed() ) {
                        r_->fixed( kFALSE );
                        this->addFloatingParameter( r_ );
                } else {
                        std::cerr << "WARNING in LauLASSRes::floatResonanceParameter: Parameter already floating.  No parameter changes made." << std::endl;
                }
        } else {
                std::cerr << "WARNING in LauLASSRes::fixResonanceParameter: Parameter name not reconised.  No parameter changes made." << std::endl;
        }
}

LauParameter* LauLASSRes::getResonanceParameter(const TString& name)
{
        if (name == "a") {
                return a_;
        } else if (name == "r") {
                return r_;
        } else {
                std::cerr << "WARNING in LauLASSRes::getResonanceParameter: Parameter name not reconised." << std::endl;
                return 0;
        }
}

void LauLASSRes::setEffectiveRange(const Double_t r)
{
        r_->value( r );
        r_->genValue( r );
        r_->initValue( r );
}

void LauLASSRes::setScatteringLength(const Double_t a)
{
        a_->value( a );
        a_->genValue( a );
        a_->initValue( a );
}