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157 | // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief psi2s -> Xi*0 Xibar*0
class BESIII_2021_I1921775 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1921775);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
declare(Beam(), "Beams");
declare(UnstableParticles(), "UFS");
declare(FinalState(), "FS");
book(_h_xi , 1, 1, 1);
book(_h_xiB, 1, 1, 2);
}
void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
for(const Particle &child : p.children()) {
if(child.children().empty()) {
nRes[child.pid()]-=1;
--ncount;
}
else
findChildren(child,nRes,ncount);
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// get the axis, direction of incoming electron
const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
Vector3 axis;
if(beams.first.pid()>0)
axis = beams.first .momentum().p3().unit();
else
axis = beams.second.momentum().p3().unit();
// types of final state particles
const FinalState& fs = apply<FinalState>(event, "FS");
map<long,int> nCount;
int ntotal(0);
for (const Particle& p : fs.particles()) {
nCount[p.pid()] += 1;
++ntotal;
}
const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
for (const Particle& p : ufs.particles(Cuts::abspid==3324)) {
if(p.children().empty()) continue;
map<long,int> nRes=nCount;
int ncount = ntotal;
findChildren(p,nRes,ncount);
bool matched=false;
// check for antiparticle
for (const Particle& p2 : ufs.particles(Cuts::pid==-p.pid())) {
if(p2.children().empty()) continue;
map<long,int> nRes2=nRes;
int ncount2 = ncount;
findChildren(p2,nRes2,ncount2);
if(ncount2==0) {
matched = true;
for(auto const & val : nRes2) {
if(val.second!=0) {
matched = false;
break;
}
}
// fond baryon and antibaryon
if(matched) {
// calc cosine
double ctheta1 = p .momentum().p3().unit().dot(axis);
double ctheta2 = p2.momentum().p3().unit().dot(axis);
if(p.pid()<0) swap(ctheta1,ctheta2);
_h_xi->fill(ctheta1);
_h_xiB->fill(ctheta2);
break;
}
}
}
if(matched) break;
}
}
pair<double,pair<double,double> > calcAlpha(Histo1DPtr hist) {
if(hist->numEntries()==0.) return make_pair(0.,make_pair(0.,0.));
double d = 3./(pow(hist->xMax(),3)-pow(hist->xMin(),3));
double c = 3.*(hist->xMax()-hist->xMin())/(pow(hist->xMax(),3)-pow(hist->xMin(),3));
double sum1(0.),sum2(0.),sum3(0.),sum4(0.),sum5(0.);
for (auto bin : hist->bins() ) {
double Oi = bin.area();
if(Oi==0.) continue;
double a = d*(bin.xMax() - bin.xMin());
double b = d/3.*(pow(bin.xMax(),3) - pow(bin.xMin(),3));
double Ei = bin.areaErr();
sum1 += a*Oi/sqr(Ei);
sum2 += b*Oi/sqr(Ei);
sum3 += sqr(a)/sqr(Ei);
sum4 += sqr(b)/sqr(Ei);
sum5 += a*b/sqr(Ei);
}
// calculate alpha
double alpha = (-c*sum1 + sqr(c)*sum2 + sum3 - c*sum5)/(sum1 - c*sum2 + c*sum4 - sum5);
// and error
double cc = -pow((sum3 + sqr(c)*sum4 - 2*c*sum5),3);
double bb = -2*sqr(sum3 + sqr(c)*sum4 - 2*c*sum5)*(sum1 - c*sum2 + c*sum4 - sum5);
double aa = sqr(sum1 - c*sum2 + c*sum4 - sum5)*(-sum3 - sqr(c)*sum4 + sqr(sum1 - c*sum2 + c*sum4 - sum5) + 2*c*sum5);
double dis = sqr(bb)-4.*aa*cc;
if(dis>0.) {
dis = sqrt(dis);
return make_pair(alpha,make_pair(0.5*(-bb+dis)/aa,-0.5*(-bb-dis)/aa));
}
else {
return make_pair(alpha,make_pair(0.,0.));
}
}
/// Normalise histograms etc., after the run
void finalize() {
normalize(_h_xi ,1.,false);
normalize(_h_xiB,1.,false);
Scatter2DPtr _h_alpha_xi;
book(_h_alpha_xi, 2,1,1);
pair<double,pair<double,double> > alpha = calcAlpha(_h_xi);
_h_alpha_xi->addPoint(0.5, alpha.first, make_pair(0.5,0.5),
make_pair(alpha.second.first,alpha.second.second) );
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h_xi,_h_xiB;
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2021_I1921775);
}
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