PDF::CParam Default_Core_Scale::Calculate(Cluster_Amplitude *const ampl)
{
DEBUG_FUNC("");
msg_Debugging()<<*ampl<<"\n";
if (ampl->Legs().size()==3 && ampl->NIn()==2) {
double kt2cmin(ampl->Leg(2)->Mom().Abs2());
return PDF::CParam(kt2cmin,kt2cmin,0.0,kt2cmin,-1);
}
double muf2(0.0), mur2(0.0), muq2(0.0);
Cluster_Amplitude *campl(Cluster(ampl->Copy()));
if (campl->Legs().size()!=ampl->Legs().size())
msg_Debugging()<<*campl<<"\n";
if (campl->Legs().size()!=4) {
double q2((campl->Leg(0)->Mom()+campl->Leg(1)->Mom()).Abs2());
Vec4D ewsum;
for (size_t i(0);i<campl->Legs().size();++i)
if (!campl->Leg(i)->Flav().Strong()) ewsum+=campl->Leg(i)->Mom();
if (ewsum==Vec4D()) ewsum=campl->Leg(0)->Mom()+campl->Leg(1)->Mom();
if (campl->NIn()==2 &&
campl->Leg(0)->Flav().Strong() &&
campl->Leg(1)->Flav().Strong()) {// HThat'/2
q2=ewsum.PPerp();
for (size_t i(0);i<campl->Legs().size();++i)
if (campl->Leg(i)->Flav().Strong())
q2+=campl->Leg(i)->Mom().PPerp();
q2=sqr(ewsum.Mass()+q2/2.0);
}
campl->Delete();
return PDF::CParam(q2,dabs(ewsum.Abs2()),0.0,q2,-1);
}
Flavour_Vector fl; fl.resize(4);
fl[0]=campl->Leg(0)->Flav();
fl[1]=campl->Leg(1)->Flav();
fl[2]=campl->Leg(2)->Flav();
fl[3]=campl->Leg(3)->Flav();
if (fl[0].Strong() && fl[1].Strong()) {// hh collision
if (fl[2].Strong() && fl[3].Strong()) {
msg_Debugging()<<"pure QCD like\n";
double s(2.0*campl->Leg(0)->Mom()*campl->Leg(1)->Mom());
double t(2.0*campl->Leg(0)->Mom()*campl->Leg(2)->Mom());
double u(2.0*campl->Leg(0)->Mom()*campl->Leg(3)->Mom());
muq2=muf2=mur2=-1.0/(1.0/s+1.0/t+1.0/u)/4.0;
}
else if (!fl[2].Strong() && !fl[3].Strong()) {
msg_Debugging()<<"DY like\n";
muq2=muf2=mur2=(campl->Leg(0)->Mom()+campl->Leg(1)->Mom()).Abs2();
}
else if (fl[2].Strong() && !fl[3].Strong()) {
msg_Debugging()<<"jV like\n";
muq2=muf2=mur2=campl->Leg(3)->Mom().MPerp2()/4.0;
}
else if (!fl[2].Strong() && fl[3].Strong()) {
msg_Debugging()<<"Vj like\n";
muq2=muf2=mur2=campl->Leg(2)->Mom().MPerp2()/4.0;
}
else THROW(fatal_error,"Internal error.");
}
else if (!fl[0].Strong() && !fl[1].Strong()) {// ll collision
if (fl[2].Strong() && fl[3].Strong()) {
msg_Debugging()<<"jets like\n";
muq2=muf2=mur2=(campl->Leg(0)->Mom()+campl->Leg(1)->Mom()).Abs2();
}
}
else {// lh collision
msg_Debugging()<<"DIS like\n";
muq2=muf2=mur2=dabs((campl->Leg(fl[0].Strong()?1:0)->Mom()+
campl->Leg(fl[2].Strong()?3:2)->Mom()).Abs2());
}
campl->Delete();
msg_Debugging()<<"\\mu_f = "<<sqrt(muf2)<<"\n"
<<"\\mu_r = "<<sqrt(mur2)<<"\n"
<<"\\mu_q = "<<sqrt(muq2)<<"\n";
return PDF::CParam(muf2,muq2,0.0,mur2,-1);
}
