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106 | // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"
namespace Rivet {
/// @brief B0 -> lambdabar p pi-
class BABAR_2009_I819092 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I819092);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
UnstableParticles ufs = UnstableParticles(Cuts::pid==511);
declare(ufs, "UFS");
DecayedParticles B0(ufs);
B0.addStable( 3122);
B0.addStable(-3122);
declare(B0, "B0");
book(_h_pol1,2,1,1);
for(unsigned int ix=0;ix<3;++ix) {
if(ix<2) book(_h_mass[ix],1,1,1+ix);
book(_h_pol2[ix],3,1,1+ix);
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
static const map<PdgId,unsigned int> & mode = { { 2212,1},{-3122,1}, {-211,1}};
DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
// loop over particles
for(unsigned int ix=0;ix<B0.decaying().size();++ix) {
if (!B0.modeMatches(ix,3,mode)) continue;
const Particle & pp = B0.decayProducts()[ix].at( 2212)[0];
const Particle & LamBar = B0.decayProducts()[ix].at(-3122)[0];
_h_mass[0]->fill( (pp.momentum()+LamBar.momentum()).mass());
// boost to B rest frame
LorentzTransform boost =
LorentzTransform::mkFrameTransformFromBeta(B0.decaying()[ix]. momentum().betaVec());
FourMomentum pLam = boost.transform(LamBar.momentum());
FourMomentum pProton = boost.transform(pp .momentum());
_h_mass[1]->fill(pLam.E());
// Lambda decay products
if(LamBar.children().size()!=2) continue;
Particle pbar;
if(LamBar.children()[0].pid()==-2212 &&
LamBar.children()[1].pid()== 211) {
pbar = LamBar.children()[0];
}
else if(LamBar.children()[1].pid()==-2212 &&
LamBar.children()[0].pid()== 211) {
pbar = LamBar.children()[1];
}
else
continue;
LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pLam.betaVec());
Vector3 axisP = boost2.transform(boost.transform(pbar.momentum())).p3().unit();
Vector3 axis1 = pLam.p3().unit();
double cTheta = axisP.dot(axis1);
_h_pol1 ->fill(pLam.E(),3.*cTheta);
_h_pol2[0]->fill(pLam.E(),3.*cTheta);
Vector3 axis2 = pLam.p3().cross(pProton.p3()).unit();
cTheta = axisP.dot(axis2);
_h_pol2[1]->fill(pLam.E(),3.*cTheta);
Vector3 axis3 = axis1.cross(axis2);
cTheta = axisP.dot(axis3);
_h_pol2[2]->fill(pLam.E(),3.*cTheta);
}
}
/// Normalise histograms etc., after the run
void finalize() {
double alpha = -0.732;
for(unsigned int ix=0;ix<2;++ix) {
if(ix<2) normalize(_h_mass[ix],1.,false);
_h_pol2[ix]->scaleY(1./alpha);
}
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h_mass[2];
Profile1DPtr _h_pol1,_h_pol2[3];
/// @}
};
RIVET_DECLARE_PLUGIN(BABAR_2009_I819092);
}
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