Rivet analyses

Mass and helicity angles in B+ → K+π+π−

Experiment: BABAR (PEP-II)

Inspire ID: 626730

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 70 (2004) 092001

Beams: * *

Beam energies: ANY

Run details: - Any process producing B+ mesons, originally Upsilon(4S) decays

Measurement of mass distributions and helicity angles in B+ → K+π+π−. The efficiency corrected, background subtracted data were read from the figures in the paper

Source code:BABAR_2004_I626730.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"

namespace Rivet {


  /// @brief B -> K pi pi
  class BABAR_2004_I626730 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2004_I626730);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid==521);
      declare(ufs, "UFS");
      DecayedParticles BP(ufs);
      BP.addStable(PID::K0S);
      declare(BP, "BP");
      for(unsigned int ix=0; ix<3; ++ix) {
    book(_h_mass2[ix],2,1,1+ix);
    book(_h_angle[ix],2,2,1+ix);
    if(ix==2) continue;
    book(_h_mass [ix],1,1,1+ix);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode   = { { 321,1}, { 211,1}, {-211,1}};
      static const map<PdgId,unsigned int> & modeCC = { {-321,1}, { 211,1}, {-211,1}};
      DecayedParticles BP = apply<DecayedParticles>(event, "BP");
      // loop over particles
      for(unsigned int ix=0;ix<BP.decaying().size();++ix) {
        int sign = BP.decaying()[ix].pid()>0 ? 1 : -1;
        if((sign>0 and BP.modeMatches(ix,3,mode)) ||
       (sign<0 and BP.modeMatches(ix,3,mode))) {
      // boost to B rest frame
      LorentzTransform boost =
        LorentzTransform::mkFrameTransformFromBeta(BP.decaying()[ix]. momentum().betaVec());
      // momenta
      FourMomentum pip  = boost.transform(BP.decayProducts()[ix].at( 211*sign)[0].momentum());
      FourMomentum pim  = boost.transform(BP.decayProducts()[ix].at(-211*sign)[0].momentum());
      FourMomentum Kp   = boost.transform(BP.decayProducts()[ix].at( 321*sign)[0].momentum());
      // mass distributions
      double mKpi = (Kp+pim).mass();
      _h_mass[0]->fill(mKpi);
      double mpipi = (pip+pim).mass();
      _h_mass[1]->fill(mpipi);
      // regions for the helicity analysis
      unsigned int imode=0;
      if(mKpi>0.816 && mKpi<0.976 && mpipi>1.5)   imode=0;
      else if(mpipi>0.9 && mpipi<1.1)             imode=1;
      else if(mKpi>0.976&& mKpi<1.8 && mpipi>1.5) imode=2;
      else continue;
      // pi+pi- resonance
      if(imode==1) {
        _h_mass2[imode]->fill(mpipi);
        FourMomentum ppipi = pim+pip;
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
        double cTheta = boost2.transform(pim).p3().unit().dot(Kp.p3().unit());
        _h_angle[imode]->fill(cTheta);
      }
      // K pi- resonance
      else {
        _h_mass2[imode]->fill(mKpi);
        FourMomentum pKpim = Kp+pim;
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pKpim.betaVec());
        double cTheta = boost2.transform(Kp).p3().unit().dot(pip.p3().unit());
        _h_angle[imode]->fill(cTheta);
      }
    }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for(unsigned int ix=0; ix<3; ++ix) {
    normalize(_h_mass2[ix],1.,false);
    normalize(_h_angle[ix],1.,false);
    if(ix==2) continue;
    normalize(_h_mass[ix],1.,false);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_mass[2],_h_mass2[3],_h_angle[3];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BABAR_2004_I626730);

}