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Bertram Kopf authoredc0b96380
EvtGenKine.cc 8.03 KiB
//--------------------------------------------------------------------------
//
// Environment:
// This software is part of the EvtGen package developed jointly
// for the BaBar and CLEO collaborations. If you use all or part
// of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/COPYRIGHT
// Copyright (C) 1998 Caltech, UCSB
//
// Module: EvtGenKine.cc
//
// Description: Tools for generating distributions of four vectors in
// phasespace
//
// Modification history:
//
// DJL/RYD September 25, 1996 Module created
//
//------------------------------------------------------------------------
//
#include <iostream>
#include "PspGen/EvtGenKine.hh"
#include "PspGen/EvtRandom.hh"
#include "PspGen/EvtVector4R.hh"
#include "PspGen/EvtConst.hh"
#include <math.h>
using std::endl;
double EvtPawt(double a,double b,double c)
{
double temp=(a*a-(b+c)*(b+c))*(a*a-(b-c)*(b-c));
if (temp<=0) {
return 0.0;
}
return sqrt(temp)/(2.0*a);
}
double EvtGenKine::PhaseSpace( int ndaug, double mass[30], EvtVector4R p4[30],
double mp )
// N body phase space routine. Send parent with
// daughters already defined ( Number and masses )
// Returns four vectors in parent frame.
{
double energy, p3, alpha, beta;
if ( ndaug == 1 ) {
p4[0].set(mass[0],0.0,0.0,0.0);
return 1.0;
}
if ( ndaug == 2 ) {
//Two body phase space
energy = ( mp*mp + mass[0]*mass[0] -
mass[1]*mass[1] ) / ( 2.0 * mp );
p3 = sqrt( energy*energy - mass[0]*mass[0] );
p4[0].set( energy, 0.0, 0.0, p3 );
energy = mp - energy;
p3 = -1.0*p3;
p4[1].set( energy, 0.0, 0.0, p3 );
//Now rotate four vectors.
alpha = EvtRandom::Flat( EvtConst::twoPi );
beta = acos(EvtRandom::Flat( -1.0, 1.0 ));
p4[0].applyRotateEuler( alpha, beta, -alpha );
p4[1].applyRotateEuler( alpha, beta, -alpha );
return 1.0;
}
if ( ndaug != 2 ) {
double wtmax=0.0;
double pm[5][30],to[4],pmin,pmax,psum,rnd[30];
double ran,wt,pa,costh,sinth,phi,p[4][30],be[4],bep,temp;
int i,il,ilr,i1,il1u,il1,il2r,ilu;
int il2=0;
for(i=0;i<ndaug;i++){
pm[4][i]=0.0;
rnd[i]=0.0;
}
pm[0][0]=mp;
pm[1][0]=0.0;
pm[2][0]=0.0;
pm[3][0]=0.0;
pm[4][0]=mp;
to[0]=mp;
to[1]=0.0;
to[2]=0.0;
to[3]=0.0;
psum=0.0;
for(i=1;i<ndaug+1;i++){
psum=psum+mass[i-1];
}
pm[4][ndaug-1]=mass[ndaug-1];
switch (ndaug) {
case 1:
wtmax=1.0/16.0;
break;
case 2:
wtmax=1.0/150.0;
break;
case 3:
wtmax=1.0/2.0;
break;
case 4:
wtmax=1.0/5.0;
break;
case 5:
wtmax=1.0/15.0;
break;
case 6:
wtmax=1.0/15.0;
break;
case 7:
wtmax=1.0/15.0;
break;
case 8: wtmax=1.0/15.0;
break;
case 9:
wtmax=1.0/15.0;
break;
case 10:
wtmax=1.0/15.0;
break;
case 11:
wtmax=1.0/15.0;
break;
case 12:
wtmax=1.0/15.0;
break;
case 13:
wtmax=1.0/15.0;
break;
case 14:
wtmax=1.0/15.0;
break;
case 15:
wtmax=1.0/15.0;
break;
default:
std::cerr << "too many daughters for phase space..." << ndaug << " "<< mp << std::endl;
break;
}
pmax=mp-psum+mass[ndaug-1];
pmin=0.0;
for(ilr=2;ilr<ndaug+1;ilr++){
il=ndaug+1-ilr;
pmax=pmax+mass[il-1];
pmin=pmin+mass[il+1-1];
wtmax=wtmax*EvtPawt(pmax,pmin,mass[il-1]);
}
do{
rnd[0]=1.0;
il1u=ndaug-1;
for (il1=2;il1<il1u+1;il1++){
ran=EvtRandom::Flat();
for (il2r=2;il2r<il1+1;il2r++){
il2=il1+1-il2r;
if (ran<=rnd[il2-1]) goto two39;
rnd[il2+1-1]=rnd[il2-1];
}
two39:
rnd[il2+1-1]=ran;
}
rnd[ndaug-1]=0.0;
wt=1.0;
for(ilr=2;ilr<ndaug+1;ilr++){
il=ndaug+1-ilr;
pm[4][il-1]=pm[4][il+1-1]+mass[il-1]+
(rnd[il-1]-rnd[il+1-1])*(mp-psum);
wt=wt*EvtPawt(pm[4][il-1],pm[4][il+1-1],mass[il-1]);
}
if (wt>wtmax) {
std::cerr << "wtmax to small in EvtPhaseSpace with "
<< ndaug <<" daughters"<< std::endl;
}
} while (wt<EvtRandom::Flat(wtmax));
ilu=ndaug-1;
for (il=1;il<ilu+1;il++){
pa=EvtPawt(pm[4][il-1],pm[4][il+1-1],mass[il-1]);
costh=EvtRandom::Flat(-1.0,1.0);
sinth=sqrt(1.0-costh*costh);
phi=EvtRandom::Flat(EvtConst::twoPi);
p[1][il-1]=pa*sinth*cos(phi);
p[2][il-1]=pa*sinth*sin(phi);
p[3][il-1]=pa*costh;
pm[1][il+1-1]=-p[1][il-1];
pm[2][il+1-1]=-p[2][il-1];
pm[3][il+1-1]=-p[3][il-1];
p[0][il-1]=sqrt(pa*pa+mass[il-1]*mass[il-1]);
pm[0][il+1-1]=sqrt(pa*pa+pm[4][il+1-1]*pm[4][il+1-1]);
}
p[0][ndaug-1]=pm[0][ndaug-1];
p[1][ndaug-1]=pm[1][ndaug-1];
p[2][ndaug-1]=pm[2][ndaug-1];
p[3][ndaug-1]=pm[3][ndaug-1];
for (ilr=2;ilr<ndaug+1;ilr++){
il=ndaug+1-ilr;
be[0]=pm[0][il-1]/pm[4][il-1];
be[1]=pm[1][il-1]/pm[4][il-1];
be[2]=pm[2][il-1]/pm[4][il-1];
be[3]=pm[3][il-1]/pm[4][il-1];
for (i1=il;i1<ndaug+1;i1++){
bep=be[1]*p[1][i1-1]+be[2]*p[2][i1-1]+
be[3]*p[3][i1-1]+be[0]*p[0][i1-1];
temp=(p[0][i1-1]+bep)/(be[0]+1.0);
p[1][i1-1]=p[1][i1-1]+temp*be[1];
p[2][i1-1]=p[2][i1-1]+temp*be[2];
p[3][i1-1]=p[3][i1-1]+temp*be[3];
p[0][i1-1]=bep;
}
}
for (ilr=0;ilr<ndaug;ilr++){
p4[ilr].set(p[0][ilr],p[1][ilr],p[2][ilr],p[3][ilr]);
}
return 1.0;
}
return 1.0;
}
double EvtGenKine::PhaseSpacePole(double M, double m1, double m2, double m3,
double a,EvtVector4R p4[10])
// generate kinematics for 3 body decays, pole for the m1,m2 mass.
{
//f1 = 1 (phasespace)
//f2 = a*(1/m12sq)^2
double m12sqmax=(M-m3)*(M-m3);
double m12sqmin=(m1+m2)*(m1+m2);
double m13sqmax=(M-m2)*(M-m2);
double m13sqmin=(m1+m3)*(m1+m3);
double v1=(m12sqmax-m12sqmin)*(m13sqmax-m13sqmin);
double v2= a*(1.0/m12sqmin-1.0/m12sqmax)*(m13sqmax-m13sqmin);
double m12sq,m13sq;
double r=v1/(v1+v2);
double m13min,m13max;
do{
m13sq=EvtRandom::Flat(m13sqmin,m13sqmax);
if (r>EvtRandom::Flat()){
m12sq=EvtRandom::Flat(m12sqmin,m12sqmax);
}
else{
m12sq=1.0/(1.0/m12sqmin-EvtRandom::Flat()*(1.0/m12sqmin-1.0/m12sqmax));
}
//kinematically allowed?
double E3star=(M*M-m12sq-m3*m3)/sqrt(4*m12sq);
double E1star=(m12sq+m1*m1-m2*m2)/sqrt(4*m12sq);
double p3star=sqrt(E3star*E3star-m3*m3);
double p1star=sqrt(E1star*E1star-m1*m1);
m13max=(E3star+E1star)*(E3star+E1star)-
(p3star-p1star)*(p3star-p1star);
m13min=(E3star+E1star)*(E3star+E1star)-
(p3star+p1star)*(p3star+p1star);
}while(m13sq<m13min||m13sq>m13max);
double E2=(M*M+m2*m2-m13sq)/(2.0*M);
double E3=(M*M+m3*m3-m12sq)/(2.0*M);
double E1=M-E2-E3;
double p1mom=sqrt(E1*E1-m1*m1);
double p3mom=sqrt(E3*E3-m3*m3);
double cost13=(2.0*E1*E3+m1*m1+m3*m3-m13sq)/(2.0*p1mom*p3mom);
//report(INFO,"EvtGen") << m13sq << endl;
//report(INFO,"EvtGen") << m12sq << endl;
//report(INFO,"EvtGen") << E1 << endl;
//report(INFO,"EvtGen") << E2 << endl;
//report(INFO,"EvtGen") << E3 << endl;
//report(INFO,"EvtGen") << p1mom << endl;
//report(INFO,"EvtGen") << p3mom << endl;
//report(INFO,"EvtGen") << cost13 << endl;
p4[2].set(E3,0.0,0.0,p3mom);
p4[0].set(E1,p1mom*sqrt(1.0-cost13*cost13),0.0,p1mom*cost13);
p4[1].set(E2,-p1mom*sqrt(1.0-cost13*cost13),0.0,-p1mom*cost13-p3mom);
//report(INFO,"EvtGen") << "p4:"<<p4[0]<<p4[1]<<p4[2]<<endl;
double alpha = EvtRandom::Flat( EvtConst::twoPi );
double beta = acos(EvtRandom::Flat( -1.0, 1.0 ));
double gamma = EvtRandom::Flat( EvtConst::twoPi );
p4[0].applyRotateEuler( alpha, beta, gamma );
p4[1].applyRotateEuler( alpha, beta, gamma );
p4[2].applyRotateEuler( alpha, beta, gamma );
return 1.0+a/(m12sq*m12sq);
}