Rivet analyses

Mass and angular distributions in B− → D0π−π0 in the ρ region

Experiment: BELLE (KEKB)

Inspire ID: 2778312

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 109 (2024) 11, L111103 - arXiv: 2404.10874

Beams: * *

Beam energies: ANY

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

Measurement of the mass and angular distribution in B− → D0π−π0 decays in the ρ region

Source code:BELLE_2024_I2778312.cc

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

namespace Rivet {


  /// @brief B -> D rho
  class BELLE_2024_I2778312 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2024_I2778312);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::pid == -521);
      declare(ufs, "UFS");
      DecayedParticles BP(ufs);
      BP.addStable(421);
      BP.addStable(111);
      declare(BP, "BP");
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      DecayedParticles BP = apply<DecayedParticles>(event, "BP");
      for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
        if (!BP.modeMatches(ix, 3, mode)) continue;
        const Particle& pim = BP.decayProducts()[ix].at(-211)[0];
        const Particle& pi0 = BP.decayProducts()[ix].at(111)[0];
        // compute the helicity angles
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
            BP.decaying()[ix].mom().betaVec());

        // pi pi mass and angle
        FourMomentum ppipi = pim.mom() + pi0.mom();
        ppipi = boost1.transform(ppipi);
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
        FourMomentum pPi = boost1.transform(pim.mom());
        FourMomentum pPi3 = boost2.transform(pPi);
        double cTheta = -pPi3.p3().unit().dot(ppipi.p3().unit());
        if (cTheta > 0.7) continue;
        _h[0]->fill(cTheta);
        _h[1]->fill(ppipi.mass() / GeV);
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2];
    const map<PdgId, unsigned int> mode = {{-211, 1}, {111, 1}, {421, 1}};
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2024_I2778312);

}