Rivet analyses

Mass distributions in B0 → KS0π+π− decays

Experiment: BABAR (PEP-II)

Inspire ID: 821188

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 80 (2009) 112001

Beams: * *

Beam energies: ANY

Run details: - Any process producing B0, originally Upsilon(4S) decay

Measurement of mass distributions in B0 → KS0π+π− decays. The data were read from the plots in the paper and may not be corrected for efficiency/acceptance, however the backgrounds shown in the paper have been subtracted.

Source code:BABAR_2009_I821188.cc

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

namespace Rivet {


  /// @brief B0 > KS0 pi+ pi-
  class BABAR_2009_I821188 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I821188);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
      declare(ufs, "UFS");
      DecayedParticles B0(ufs);
      B0.addStable(PID::K0S);
      declare(B0, "B0");
      // histograms
      for (unsigned int ix = 0; ix < 2; ++ix)
        for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 1 + ix, 1, 1 + iy);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{310, 1}, {211, 1}, {-211, 1}};
      DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
      // loop over particles
      for (unsigned int ix = 0; ix < B0.decaying().size(); ++ix) {
        if (!B0.modeMatches(ix, 3, mode)) continue;
        int sign = B0.decaying()[ix].pid() > 0 ? 1 : -1;
        // boost to B rest frame
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
            B0.decaying()[ix].momentum().betaVec());
        // momenta
        FourMomentum pip = boost.transform(B0.decayProducts()[ix].at(211 * sign)[0].momentum());
        FourMomentum pim = boost.transform(B0.decayProducts()[ix].at(-211 * sign)[0].momentum());
        FourMomentum K0 = boost.transform(B0.decayProducts()[ix].at(310)[0].momentum());
        // pi+pi- resonance
        FourMomentum ppipi = pim + pip;
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
        double cTheta = boost2.transform(pim).p3().unit().dot(K0.p3().unit());
        if (cTheta > 0.)
          _h[0][0]->fill(ppipi.mass());
        else
          _h[0][1]->fill(ppipi.mass());
        // K pi- resonance
        FourMomentum pKpim = K0 + pim;
        boost2 = LorentzTransform::mkFrameTransformFromBeta(pKpim.betaVec());
        cTheta = boost2.transform(K0).p3().unit().dot(pip.p3().unit());
        if (cTheta > 0.)
          _h[1][0]->fill(pKpim.mass());
        else
          _h[1][1]->fill(pKpim.mass());
        // K pi+ resonance
        FourMomentum pKpip = K0 + pip;
        boost2 = LorentzTransform::mkFrameTransformFromBeta(pKpip.betaVec());
        cTheta = boost2.transform(pip).p3().unit().dot(pim.p3().unit());
        if (cTheta > 0.)
          _h[1][0]->fill(pKpip.mass());
        else
          _h[1][1]->fill(pKpip.mass());
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2][2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2009_I821188);

}