Rivet analyses

Kinematic distributions in Υ2(1D) → π+π−Υ(1S)

Experiment: BABAR (PEP-II)

Inspire ID: 850492

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 82 (2010) 111102

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon_2(1D)

Measurement of the kinematic distributions in Υ2(1D) → π+π−Υ(1S) by BABAR. The data were read from the paper and may not have been corrected for acceptance.

Source code:BABAR_2010_I850492.cc

// -*- 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);

}