// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief B0 -> a1+ a1-
class BABAR_2009_I825406 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I825406);
/// @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, "B0");
// histograms
book(_p,1,1,1);
}
void findChildren(const Particle & p, Particles & pim, Particles & pip,
Particles & pi0, 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::PI0) {
pi0.push_back(child);
ncount+=1;
}
else if(child.children().empty()) {
ncount+=1;
}
else
findChildren(child,pim,pip,pi0,ncount);
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
Particles B0 = apply<UnstableParticles>(event, "B0").particles();
for(const Particle & p : B0) {
// skip cases with mixing
if(p.children().size()==1 && p.children()[0].abspid()==p.abspid()) continue;
// particle antiparticle pair of a_1
if(p.children().size()!=2 || p.children()[0].pid()!=-p.children()[1].pid() ||
p.children()[0].abspid()!=20213) continue;
Particle a1p = p.children()[0], a1m = p.children()[1];
if( (p.pid()>0&&a1p.pid()<0) || (p.pid()<0&&a1p.pid()>0) ) swap(a1p,a1m);
Particles pip,pim,pi0;
unsigned int ncount=0;
findChildren(a1p,pim,pip,pi0,ncount);
if(ncount!=3 || pip.size()!=2 || pim.size()!=1) continue;
LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
FourMomentum pa1p = boost.transform(a1p.momentum());
FourMomentum pa1m = boost.transform(a1m.momentum());
LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pa1p.betaVec());
FourMomentum ppip = boost2.transform(boost.transform(pip[0].momentum()));
FourMomentum ppim = boost2.transform(boost.transform(pim[0].momentum()));
Vector3 n = ppip.p3().cross(ppim.p3()).unit();
double cTheta = n.dot(pa1m.p3().unit());
_p->fill(5.28,(2.-5.*sqr(cTheta)));
}
}
/// Normalise histograms etc., after the run
void finalize() {
}
/// @}
/// @name Histograms
/// @{
Profile1DPtr _p;
/// @}
};
RIVET_DECLARE_PLUGIN(BABAR_2009_I825406);
}