LauLASSBWRes.cc

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/*
Copyright 2008 University of Warwick

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/*
Laura++ package authors:
John Back
Paul Harrison
Thomas Latham
*/

#include <iostream>

#include "LauConstants.hh"
#include "LauLASSBWRes.hh"
#include "LauResonanceInfo.hh"

ClassImp(LauLASSBWRes)


LauLASSBWRes::LauLASSBWRes(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)
{
        // Default values for LASS parameters
        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_ );
        }
}

LauLASSBWRes::~LauLASSBWRes()
{
}

void LauLASSBWRes::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 LauLASSBWRes::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 LauLASSBWRes::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 LauLASSBWRes::resAmp(Double_t mass, Double_t /*spinTerm*/)
{
        LauComplex resAmplitude(0.0, 0.0);

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

        // 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;

        return resAmplitude;
}

const std::vector<LauParameter*>& LauLASSBWRes::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 LauLASSBWRes::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 LauLASSBWRes::setResonanceParameter : Setting LASS Scattering Length = " << this->getScatteringLength() << std::endl;
        } else if (name == "r") {
                this->setEffectiveRange(value);
                std::cout << "INFO in LauLASSBWRes::setResonanceParameter : Setting LASS Effective Range = " << this->getEffectiveRange() << std::endl;
        } else {
                std::cerr << "WARNING in LauLASSBWRes::setResonanceParameter: Parameter name not reconised.  No parameter changes made." << std::endl;
        }
}

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

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

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

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