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| // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief J/psi to p pbar n nbar
class BESIII_2012_I1113599 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2012_I1113599);
/// @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 histograms
book(_h_proton , "ctheta_p",20,-1.,1.);
book(_h_neutron, "ctheta_n",20,-1.,1.);
}
/// 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);
Particle outgoing;
for (const Particle& p : fs.particles()) {
nCount[p.pid()] += 1;
if(p.pid()==2212 || p.pid()==2112)
outgoing = p;
++ntotal;
}
if(ntotal==2) {
if(nCount[2212]==1 && nCount[-2212]==1) {
_h_proton->fill(outgoing.momentum().p3().unit().dot(axis));
}
else if(nCount[2112]==1 && nCount[-2112]==1) {
_h_neutron->fill(outgoing.momentum().p3().unit().dot(axis));
}
}
}
pair<double,pair<double,double> > calcAlpha(Histo1DPtr hist) {
if(hist->numEntries()==0.) return make_pair(0.,make_pair(0.,0.));
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 = 1.5*(bin.xMax() - bin.xMin());
double b = 0.5*(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 = (-3*sum1 + 9*sum2 + sum3 - 3*sum5)/(sum1 - 3*sum2 + 3*sum4 - sum5);
// and error
double cc = -pow((sum3 + 9*sum4 - 6*sum5),3);
double bb = -2*sqr(sum3 + 9*sum4 - 6*sum5)*(sum1 - 3*sum2 + 3*sum4 - sum5);
double aa = sqr(sum1 - 3*sum2 + 3*sum4 - sum5)*(-sum3 - 9*sum4 + sqr(sum1 - 3*sum2 + 3*sum4 - sum5) + 6*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() {
// proton
normalize(_h_proton );
pair<double,pair<double,double> > alpha = calcAlpha(_h_proton);
Scatter2DPtr _h_alpha_proton;
book(_h_alpha_proton,1,1,1);
_h_alpha_proton->addPoint(0.5, alpha.first, make_pair(0.5,0.5),
make_pair(alpha.second.first,alpha.second.second) );
// neutron
normalize(_h_neutron);
alpha = calcAlpha(_h_neutron);
Scatter2DPtr _h_alpha_neutron;
book(_h_alpha_neutron, 1,1,2);
_h_alpha_neutron->addPoint(0.5, alpha.first, make_pair(0.5,0.5),
make_pair(alpha.second.first,alpha.second.second) );
}
//@}
/// @name Histograms
//@{
Histo1DPtr _h_proton,_h_neutron;
//@}
};
// The hook for the plugin system
RIVET_DECLARE_PLUGIN(BESIII_2012_I1113599);
}
|