LauBreitWignerRes.cc

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// Copyright University of Warwick 2004 - 2013.
// 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

//****************************************************************************
// Class for defining the Breit-Wigner resonance model
//****************************************************************************

// --CLASS DESCRIPTION [MODEL] --
// Class for defining the Breit-Wigner resonance model

#include "LauBreitWignerRes.hh"

ClassImp(LauBreitWignerRes)


LauBreitWignerRes::LauBreitWignerRes(TString resName, Double_t resMass, Double_t resWidth, Int_t resSpin,
                Int_t resCharge, Int_t resPairAmpInt, const LauDaughters* daughters) :
        LauAbsResonance(resName, resMass, resWidth, resSpin, resCharge, resPairAmpInt, daughters)
{
}

LauBreitWignerRes::~LauBreitWignerRes()
{
}

void LauBreitWignerRes::initialise()
{
}

LauComplex LauBreitWignerRes::resAmp(Double_t mass, Double_t spinTerm)
{
        // This function returns the complex dynamical amplitude for a Breit-Wigner resonance,
        // given the invariant mass and cos(helicity) values.

        Double_t resMass = this->getMass();
        Double_t deltaM = mass - resMass;

        Double_t resWidthO2 = 0.5 * this->getWidth();
        Double_t resWidthO2Sq = resWidthO2*resWidthO2;

        LauComplex resAmplitude(deltaM, resWidthO2);

        resAmplitude.rescale(spinTerm/(deltaM*deltaM + resWidthO2Sq));

        return resAmplitude;
}