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122 | // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief B -> K X(3872)
class BELLE_2011_I916712 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2011_I916712);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// set the PDG code
_pid = getOption<double>("PID", 9030443);
// projections
declare(UnstableParticles(Cuts::abspid==511 ||
Cuts::abspid==521), "UFS");
// histograms
for(unsigned int ix=0;ix<4;++ix)
book(_h[ix],1+ix,1,1);
}
void findChildren(const Particle & p, Particles & pim, Particles & pip,
Particles & Jpsi, unsigned int &ncount) {
for( const Particle &child : p.children()) {
if(child.pid()==PID::PIPLUS) {
pip.push_back(child);
ncount+=1;
}
else if(child.pid()==PID::PIMINUS) {
pim.push_back(child);
ncount+=1;
}
else if(child.pid()==PID::JPSI) {
Jpsi.push_back(child);
ncount+=1;
}
else if(child.children().empty()) {
ncount+=1;
}
else
findChildren(child,pim,pip,Jpsi,ncount);
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
for(const Particle & p : apply<UnstableParticles>(event, "UFS").particles()) {
if(p.children().empty()) continue;
if(p.children().size()==1) continue;
if(p.children().size()!=2) continue;
Particle K,X;
if(p.children()[0].pid()==_pid) {
X = p.children()[0];
K = p.children()[1];
}
else if(p.children()[1].pid()==_pid) {
X = p.children()[1];
K = p.children()[0];
}
else continue;
if(K.abspid()!=311 && K.abspid()!=321 &&
K.abspid()!=310 && K.abspid()!=130) continue;
// X(3872) decay
unsigned int ncount=0;
Particles pip,pim,Jpsi;
findChildren(X,pim,pip,Jpsi,ncount);
if( ncount!=3 || !(pim.size()==1 && pip.size()==1 && Jpsi.size()==1)) continue;
_h[3]->fill((pip[0].momentum()+pim[0].momentum()).mass());
LorentzTransform boostB = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
Vector3 axisX = -boostB.transform(K.momentum()).p3().unit();
FourMomentum pX = boostB.transform(X .momentum());
LorentzTransform boostX = LorentzTransform::mkFrameTransformFromBeta(pX.betaVec());
FourMomentum pPsi = boostX.transform(boostB.transform(Jpsi[0].momentum()));
double cTheta = axisX.dot(pPsi.p3().unit());
_h[0]->fill(cTheta);
// finally the leptons from J/psi decay
if(Jpsi[0].children().size()!=2) vetoEvent;
if(Jpsi[0].children()[0].pid()!=-Jpsi[0].children()[1].pid()) vetoEvent;
if(Jpsi[0].children()[0].abspid()!=PID::EMINUS &&
Jpsi[0].children()[0].abspid()!=PID::MUON) vetoEvent;
Particle lm = Jpsi[0].children()[0];
Particle lp = Jpsi[0].children()[1];
Vector3 axispi = boostX.transform(boostB(pip[0].momentum())).p3().unit();
Vector3 axisZ = axispi.cross(axisX).unit();
Vector3 axisL = boostX.transform(boostB(lp.momentum())).p3().unit();
_h[2]->fill(abs(axisZ.dot(axisL)));
_h[1]->fill(abs(axisX.dot(axisL)));
}
}
/// Normalise histograms etc., after the run
void finalize() {
for(unsigned int ix=0;ix<4;++ix)
normalize(_h[ix],1.,false);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[4];
int _pid;
/// @}
};
RIVET_DECLARE_PLUGIN(BELLE_2011_I916712);
}
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