// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"
namespace Rivet {
/// @brief Upsilon_2 -> pi+ pi- Upsilon
class BABAR_2010_I850492 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2010_I850492);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
UnstableParticles ufs = UnstableParticles(Cuts::pid==20555);
declare(ufs, "UFS");
DecayedParticles Upsilon2(ufs);
Upsilon2.addStable(PID::PI0);
Upsilon2.addStable(553);
declare(Upsilon2, "Upsilon2");
for(unsigned int ix=0;ix<3;++ix)
book(_h[ix],1,1,1+ix);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
static const map<PdgId,unsigned int> & mode = { { 211,1}, {-211,1}, {553,1} };
DecayedParticles Upsilon2 = apply<DecayedParticles>(event, "Upsilon2");
// loop over particles
for(unsigned int ix=0;ix<Upsilon2.decaying().size();++ix) {
if ( !Upsilon2.modeMatches(ix,3,mode) ) continue;
const Particle & pip= Upsilon2.decayProducts()[ix].at( 211)[0];
const Particle & pim= Upsilon2.decayProducts()[ix].at(-211)[0];
const Particle & ups= Upsilon2.decayProducts()[ix].at( 553)[0];
FourMomentum ptot = pip.momentum()+pim.momentum();
_h[0]->fill(ptot.mass());
// boost to Upsilon_2 rest frame
LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(Upsilon2.decaying()[ix].momentum().betaVec());
FourMomentum pDir = boost.transform(ptot);
Matrix3 ptoz(-pDir.p3().unit(), Vector3(0,0,1));
boost.preMult(ptoz);
FourMomentum p2 = boost.transform(ups.momentum());
FourMomentum ppip = boost.transform(pip.momentum());
FourMomentum ppim = boost.transform(pim.momentum());
ptot = ppip+ppim;
// pion angle
LorentzTransform boostPi = LorentzTransform::mkFrameTransformFromBeta(ptot.betaVec());
Vector3 axisPi = boostPi.transform(ppip).p3().unit();
double cosPi = axisPi.dot(ptot.p3().unit());
_h[2]->fill(abs(cosPi));
if(ups.children().size()!=2) continue;
Particle ep,em;
if ( ups.children()[0].pid()==-ups.children()[1].pid() &&
(ups.children()[0].abspid()==11 || ups.children()[0].abspid()==13)) {
ep = ups.children()[0];
em = ups.children()[1];
}
else
continue;
if(em.pid()<0) swap(ep,em);
LorentzTransform boostUps = LorentzTransform::mkFrameTransformFromBeta(p2.betaVec());
FourMomentum pe = boost.transform(ep .momentum());
Vector3 axisE = boostUps.transform(pe).p3().unit();
axisPi.setZ(0.);
axisE.setZ(0.);
double chi = abs(atan2(axisE.cross(axisPi).dot(p2.p3().unit()), axisE.dot(axisPi)));
if(chi>M_PI) chi=2.*M_PI-chi;
_h[1]->fill(chi);
}
}
/// Normalise histograms etc., after the run
void finalize() {
for(unsigned int ix=0;ix<3;++ix)
normalize(_h[ix],1.,false);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[3];
/// @}
};
RIVET_DECLARE_PLUGIN(BABAR_2010_I850492);
}