Rivet analyses

title: BESIII_2018_I1705754

Kinematic distributions in $D^0\to \bar{K}^0\pi^- e^+\nu_e$

Experiment: BESIII (BEPC)

Inspire ID: 1705754

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 99 (2019) 1, 011103

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0

Measurement of the kinematic distributions in $D^0\to \bar{K}^0\pi^- e^+\nu_e$ by BES-III. N.B. the plots where read from the paper and may not have been corrected for acceptance.

Source code:BESIII_2018_I1705754.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D0 -> Kbar0 pi- e+ nu_e class BESIII_2018_I1705754 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1705754);


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

/// Book histograms and initialise projections before the run
void init() {

  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 421);
  declare(ufs, "UFS");
  DecayedParticles D0(ufs);
  D0.addStable(PID::PI0);
  D0.addStable(PID::K0S);
  D0.addStable(PID::ETA);
  D0.addStable(PID::ETAPRIME);
  declare(D0, "D0");

  // Book histograms
  for (unsigned int ix = 0; ix < 5; ++ix) book(_h[ix], 1, 1, 1 + ix);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode1 = {{310, 1}, {-211, 1}, {-11, 1}, {12, 1}};
  static const map<PdgId, unsigned int>& mode2 = {{130, 1}, {-211, 1}, {-11, 1}, {12, 1}};
  static const map<PdgId, unsigned int>& mode3 = {{-311, 1}, {-211, 1}, {-11, 1}, {12, 1}};
  DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
  // loop over particles
  for (unsigned int ix = 0; ix < D0.decaying().size(); ++ix) {
    Particle K0;
    if (D0.modeMatches(ix, 4, mode1))
      K0 = D0.decayProducts()[ix].at(310)[0];
    else if (D0.modeMatches(ix, 4, mode2))
      K0 = D0.decayProducts()[ix].at(130)[0];
    else if (D0.modeMatches(ix, 4, mode3))
      K0 = D0.decayProducts()[ix].at(-311)[0];
    else
      continue;
    const Particle& pim = D0.decayProducts()[ix].at(-211)[0];
    const Particle& ep = D0.decayProducts()[ix].at(-11)[0];
    const Particle& nue = D0.decayProducts()[ix].at(12)[0];
    FourMomentum pKstar = K0.momentum() + pim.momentum();
    _h[0]->fill(pKstar.mass());
    FourMomentum qq = D0.decaying()[ix].momentum() - pKstar;
    _h[1]->fill(qq.mass2());
    // boost momenta to D0 rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        D0.decaying()[ix].momentum().betaVec());
    FourMomentum pKS = boost.transform(pKstar);
    Matrix3 ptoz(-pKS.p3().unit(), Vector3(0, 0, 1));
    boost.preMult(ptoz);
    // the momenta in frane to W along z
    FourMomentum pD = boost.transform(D0.decaying()[ix].momentum());
    FourMomentum pK = boost.transform(K0.momentum());
    FourMomentum ppi = boost.transform(pim.momentum());
    FourMomentum pe = boost.transform(ep.momentum());
    FourMomentum pnu = boost.transform(nue.momentum());
    pKstar = pK + ppi;
    qq = pD - pKstar;
    LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
    Vector3 axisK = boostK.transform(pK).p3().unit();
    _h[3]->fill(axisK.dot(pKstar.p3().unit()));
    LorentzTransform boostW = LorentzTransform::mkFrameTransformFromBeta(qq.betaVec());
    Vector3 axisE = boostW.transform(pe).p3().unit();
    _h[2]->fill(axisE.dot(qq.p3().unit()));
    axisK.setZ(0.);
    axisE.setZ(0.);
    double chi = atan2(axisE.cross(axisK).dot(qq.p3().unit()), axisE.dot(axisK));
    _h[4]->fill(chi);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 5; ++ix) normalize(_h[ix]);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[5];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2018_I1705754);

} ```