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/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.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);

}