Rivet analyses

mass and angular distributions in B0 → p(Λ̄0, Σ̄0)π− decays

Experiment: BELLE (KEKB)

Inspire ID: 2663731

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2305.18821

Beams: * *

Beam energies: ANY

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

Measurement of the differential branching ratio with respect to the baryon pair invariant mass for B0 → p(Λ̄0, Σ̄0)π−. The differential branching ratio with respect to the proton helicity angle is also measured in the threshold region, i.e. for the baryon pair mass <2.8 GeV. The data were read from the tables in the paper.

Source code:BELLE_2023_I2663731.cc

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

namespace Rivet {


  /// @brief B0 -> lambdabar/Sigmabar0 p pi-
  class BELLE_2023_I2663731 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2023_I2663731);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 511);
      declare(ufs, "UFS");
      DecayedParticles B0(ufs);
      B0.addStable(3122);
      B0.addStable(-3122);
      B0.addStable(3212);
      B0.addStable(-3212);
      declare(B0, "B0");
      // histos
      for (unsigned int ix = 0; ix < 2; ++ix) {
        book(_h_m[ix], 1, 1, 1 + ix);
        book(_h_theta[ix], 2, 1, 1 + ix);
      }
      book(_cB, "/TMP/nB");
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
      // loop over particles
      for (unsigned int ix = 0; ix < B0.decaying().size(); ++ix) {
        _cB->fill();
        unsigned int imode = 0;
        if (B0.modeMatches(ix, 3, mode1))
          imode = 0;
        else if (B0.modeMatches(ix, 3, mode2))
          imode = 1;
        else
          continue;
        const Particle& pp = B0.decayProducts()[ix].at(2212)[0];
        const Particle& ppim = B0.decayProducts()[ix].at(-211)[0];
        const Particle& LamBar = B0.decayProducts()[ix].at(imode == 0 ? -3122 : -3212)[0];
        double mBB = (pp.mom() + LamBar.mom()).mass();
        _h_m[imode]->fill(mBB);
        if (mBB > 2.8) continue;
        // boost to B rest frame
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
            B0.decaying()[ix].mom().betaVec());
        FourMomentum pLam = boost.transform(LamBar.mom());
        FourMomentum pProton = boost.transform(pp.mom());
        Vector3 axis1 = boost.transform(ppim.mom()).p3().unit();
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta((pLam + pProton).betaVec());
        Vector3 axis2 = boost2.transform(pProton).p3().unit();
        _h_theta[imode]->fill(axis1.dot(axis2));
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h_m, 1.e6 / *_cB);
      scale(_h_theta, 1.e6 / *_cB);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_m[2], _h_theta[2];
    CounterPtr _cB;
    const map<PdgId, unsigned int> mode1 = {{2212, 1}, {-3122, 1}, {-211, 1}};
    const map<PdgId, unsigned int> mode2 = {{2212, 1}, {-3212, 1}, {-211, 1}};
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2023_I2663731);

}