EvtParticle* EvtParticleFactory::particleFactory(EvtId id,
EvtVector4R p4){
EvtSpinDensity rho;
rho.setDiag(EvtSpinType::getSpinStates(EvtPDL::getSpinType(id)));
return particleFactory(id,p4,rho);
}
double EvtSemiLeptonicAmp::CalcMaxProb( EvtId parent, EvtId meson,
EvtId lepton, EvtId nudaug,
EvtSemiLeptonicFF *FormFactors ) {
//This routine takes the arguements parent, meson, and lepton
//number, and a form factor model, and returns a maximum
//probability for this semileptonic form factor model. A
//brute force method is used. The 2D cos theta lepton and
//q2 phase space is probed.
//Start by declaring a particle at rest.
//It only makes sense to have a scalar parent. For now.
//This should be generalized later.
EvtScalarParticle *scalar_part;
EvtParticle *root_part;
scalar_part=new EvtScalarParticle;
//cludge to avoid generating random numbers!
scalar_part->noLifeTime();
EvtVector4R p_init;
p_init.set(EvtPDL::getMass(parent),0.0,0.0,0.0);
scalar_part->init(parent,p_init);
root_part=(EvtParticle *)scalar_part;
root_part->setDiagonalSpinDensity();
EvtParticle *daughter, *lep, *trino;
EvtAmp amp;
EvtId listdaug[3];
listdaug[0] = meson;
listdaug[1] = lepton;
listdaug[2] = nudaug;
amp.init(parent,3,listdaug);
root_part->makeDaughters(3,listdaug);
daughter=root_part->getDaug(0);
lep=root_part->getDaug(1);
trino=root_part->getDaug(2);
//cludge to avoid generating random numbers!
daughter->noLifeTime();
lep->noLifeTime();
trino->noLifeTime();
//Initial particle is unpolarized, well it is a scalar so it is
//trivial
EvtSpinDensity rho;
rho.setDiag(root_part->getSpinStates());
double mass[3];
double m = root_part->mass();
EvtVector4R p4meson, p4lepton, p4nu, p4w;
double q2min;
double q2max;
double q2, elepton, plepton;
int i,j;
double erho,prho,costl;
double maxfoundprob = 0.0;
double prob = -10.0;
int massiter;
for (massiter=0;massiter<3;massiter++){
mass[0] = EvtPDL::getMeanMass(meson);
mass[1] = EvtPDL::getMeanMass(lepton);
mass[2] = EvtPDL::getMeanMass(nudaug);
if ( massiter==1 ) {
mass[0] = EvtPDL::getMinMass(meson);
}
if ( massiter==2 ) {
mass[0] = EvtPDL::getMaxMass(meson);
if ( (mass[0]+mass[1]+mass[2])>m) mass[0]=m-mass[1]-mass[2]-0.00001;
}
q2min = mass[1]*mass[1];
q2max = (m-mass[0])*(m-mass[0]);
//loop over q2
for (i=0;i<25;i++) {
q2 = q2min + ((i+0.5)*(q2max-q2min))/25.0;
erho = ( m*m + mass[0]*mass[0] - q2 )/(2.0*m);
prho = sqrt(erho*erho-mass[0]*mass[0]);
p4meson.set(erho,0.0,0.0,-1.0*prho);
p4w.set(m-erho,0.0,0.0,prho);
//This is in the W rest frame
elepton = (q2+mass[1]*mass[1])/(2.0*sqrt(q2));
plepton = sqrt(elepton*elepton-mass[1]*mass[1]);
double probctl[3];
for (j=0;j<3;j++) {
costl = 0.99*(j - 1.0);
//These are in the W rest frame. Need to boost out into
//the B frame.
p4lepton.set(elepton,0.0,
plepton*sqrt(1.0-costl*costl),plepton*costl);
p4nu.set(plepton,0.0,
-1.0*plepton*sqrt(1.0-costl*costl),-1.0*plepton*costl);
EvtVector4R boost((m-erho),0.0,0.0,1.0*prho);
p4lepton=boostTo(p4lepton,boost);
p4nu=boostTo(p4nu,boost);
//Now initialize the daughters...
daughter->init(meson,p4meson);
lep->init(lepton,p4lepton);
trino->init(nudaug,p4nu);
CalcAmp(root_part,amp,FormFactors);
//Now find the probability at this q2 and cos theta lepton point
//and compare to maxfoundprob.
//Do a little magic to get the probability!!
prob = rho.normalizedProb(amp.getSpinDensity());
probctl[j]=prob;
}
//probclt contains prob at ctl=-1,0,1.
//prob=a+b*ctl+c*ctl^2
double a=probctl[1];
double b=0.5*(probctl[2]-probctl[0]);
double c=0.5*(probctl[2]+probctl[0])-probctl[1];
prob=probctl[0];
if (probctl[1]>prob) prob=probctl[1];
if (probctl[2]>prob) prob=probctl[2];
if (fabs(c)>1e-20){
double ctlx=-0.5*b/c;
if (fabs(ctlx)<1.0){
double probtmp=a+b*ctlx+c*ctlx*ctlx;
if (probtmp>prob) prob=probtmp;
}
}
if ( prob > maxfoundprob ) {
maxfoundprob = prob;
}
}
if ( EvtPDL::getWidth(meson) <= 0.0 ) {
//if the particle is narrow dont bother with changing the mass.
massiter = 4;
}
}
root_part->deleteTree();
maxfoundprob *=1.1;
return maxfoundprob;
}