Rivet analyses

Mass distributions in B− → D+π−π−

Experiment: BABAR (PEP-II)

Inspire ID: 810694

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 79 (2009) 112004

Beams: * *

Beam energies: ANY

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

Measurement of mass and angular distributions in B− → D+π−π−. The data were read from the plots in the paper and may not be corrected for acceptance/efficiency, however the backgrounds given in the paper were subtracted.

Source code:BABAR_2009_I810694.cc

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

namespace Rivet {


  /// @brief B- > D+ pi-pi-
  class BABAR_2009_I810694 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I810694);


    /// @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( 411);
      BP.addStable(-411);
      declare(BP, "BP");
      // histograms
      for(unsigned int ix=0;ix<3;++ix) {
    if(ix<2) book(_h_angle[ix],2,1,1+ix);
    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   = { { -411,1},{ 211,2}};
      static const map<PdgId,unsigned int> & modeCC = { {  411,1},{-211,2}};
      DecayedParticles BP = apply<DecayedParticles>(event, "BP");
      // loop over particles
      for(unsigned int ix=0;ix<BP.decaying().size();++ix) {
    int sign=1;
        if      (BP.modeMatches(ix,3,mode  )) sign= 1;
        else if (BP.modeMatches(ix,3,modeCC)) sign=-1;
    else continue;
        const Particle  & Dp  = BP.decayProducts()[ix].at(-sign*411)[0];
    const Particles & pim = BP.decayProducts()[ix].at( sign*211);
    _h_mass[2]->fill((pim[0].momentum()+pim[1].momentum()).mass2());
    // boost to B rest frame
    LorentzTransform boost =
      LorentzTransform::mkFrameTransformFromBeta(BP.decaying()[ix]. momentum().betaVec());
    FourMomentum pD    = boost.transform(Dp.momentum());
    FourMomentum ppi[2] = {boost.transform(pim[0].momentum()),boost.transform(pim[1].momentum())};
    double m2Dpi[2];
    for(unsigned int ix=0;ix<2;++ix) {
      m2Dpi[ix] = (pim[ix].momentum()+Dp.momentum()).mass2();
      if( (m2Dpi[ix]>4.5 && m2Dpi[ix]<5.5) ||
          (m2Dpi[ix]>5.9 && m2Dpi[ix]<6.2) ) {
        FourMomentum pDpi = pD+pim[ix];
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDpi.betaVec());
        Vector3 axis1 = boost2.transform(ppi[ix]).p3().unit();
        Vector3 axis2 = (ix==0 ? ppi[1] : ppi[0]).p3().unit();
        double cTheta = axis1.dot(axis2);
        if(m2Dpi[ix]<5.5)
          _h_angle[0]->fill(cTheta);
        else
          _h_angle[1]->fill(cTheta);
      }
    }
    if(m2Dpi[0]>m2Dpi[1]) {
      _h_mass[1]->fill(m2Dpi[0]);
      _h_mass[0]->fill(m2Dpi[1]);
    }
    else {
      _h_mass[0]->fill(m2Dpi[0]);
      _h_mass[1]->fill(m2Dpi[1]);
    }
      }
    }


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

    /// @}


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


  };


  RIVET_DECLARE_PLUGIN(BABAR_2009_I810694);

}