Rivet analyses

Mass and angular distributions in B+ → K+ηγ decays

Experiment: BELLE (KEKB)

Inspire ID: 1663447

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 97 (2018) 9, 092003

Beams: * *

Beam energies: ANY

Run details: - Any process producing B+, originally Upsilno(4S) decay

Mass and angular distributions in B+ → K+ηγ decays. Data were read from the plots in the paper, but are background subtracted and efficiency corrected.

Source code:BELLE_2018_I1663447.cc

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

namespace Rivet {


  /// @brief B+ -> K+ eta gamma
  class BELLE_2018_I1663447 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2018_I1663447);


    /// @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(PID::ETA);
      declare(BP, "BP");
      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 = {{221, 1}, {321, 1}, {22, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{221, 1}, {-321, 1}, {22, 1}};
      DecayedParticles BP = apply<DecayedParticles>(event, "BP");
      // loop over particles
      for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
        int sign = 1;
        if (BP.decaying()[ix].pid() > 0 && BP.modeMatches(ix, 3, mode)) {
          sign = 1;
        }
        else if (BP.decaying()[ix].pid() < 0 && BP.modeMatches(ix, 3, modeCC)) {
          sign = -1;
        }
        else
          continue;
        const Particle& Kp = BP.decayProducts()[ix].at(sign * 321)[0];
        const Particle& eta = BP.decayProducts()[ix].at(221)[0];
        const Particle& gamma = BP.decayProducts()[ix].at(22)[0];
        FourMomentum pKeta = Kp.momentum() + eta.momentum();
        double mass = pKeta.mass();
        LorentzTransform boostB = LorentzTransform::mkFrameTransformFromBeta(
            BP.decaying()[ix].momentum().betaVec());
        pKeta = boostB.transform(pKeta);
        LorentzTransform boostKeta = LorentzTransform::mkFrameTransformFromBeta(pKeta.betaVec());
        FourMomentum pK = boostKeta.transform(boostB.transform(Kp.momentum()));
        FourMomentum pGamma = boostB.transform(gamma.momentum());
        double cTheta = pK.p3().unit().dot(pGamma.p3().unit());
        for (unsigned int iy = 0; iy < 2; ++iy) {
          _h[0][iy]->fill(cTheta);
          _h[1][iy]->fill(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(BELLE_2018_I1663447);

}