Rivet analyses

title: BESIII_2024_I2825816

Kinematic distributions in $D^0\to \pi^-\pi^0 e^+\nu_e$

Experiment: BESIII (BEPC)

Inspire ID: 2825816

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 110 (2024) 11, 112018 - arXiv: 2409.04276

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0

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

Source code:BESIII_2024_I2825816.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D0 -> pi pi semileptonic class BESIII_2024_I2825816 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2825816);


/// @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 DD(ufs);
  DD.addStable(PID::PI0);
  DD.addStable(PID::K0S);
  DD.addStable(PID::ETA);
  DD.addStable(PID::ETAPRIME);
  declare(DD, "DD");
  // 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>& mode = {{111, 1}, {-211, 1}, {-11, 1}, {12, 1}};
  DecayedParticles DD = apply<DecayedParticles>(event, "DD");
  // loop over particles
  for (unsigned int ix = 0; ix < DD.decaying().size(); ++ix) {
    if (!DD.modeMatches(ix, 4, mode)) continue;
    const Particle& pi0 = DD.decayProducts()[ix].at(111)[0];
    const Particle& pim = DD.decayProducts()[ix].at(-211)[0];
    const Particle& ep = DD.decayProducts()[ix].at(-11)[0];
    const Particle& nue = DD.decayProducts()[ix].at(12)[0];
    FourMomentum pRho = pi0.momentum() + pim.momentum();
    _h[0]->fill(pRho.mass());
    FourMomentum qq = DD.decaying()[ix].momentum() - pRho;
    _h[1]->fill(qq.mass2());
    // boost momenta to D rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        DD.decaying()[ix].momentum().betaVec());
    FourMomentum pPP = boost.transform(pRho);
    Matrix3 ptoz(-pPP.p3().unit(), Vector3(0, 0, 1));
    boost.preMult(ptoz);
    // the momenta in frane to W along z
    FourMomentum pD = boost.transform(DD.decaying()[ix].momentum());
    FourMomentum ppi0 = boost.transform(pi0.momentum());
    FourMomentum ppim = boost.transform(pim.momentum());
    FourMomentum pe = boost.transform(ep.momentum());
    FourMomentum pnu = boost.transform(nue.momentum());
    pRho = ppi0 + ppim;
    qq = pD - pRho;
    LorentzTransform boostRho = LorentzTransform::mkFrameTransformFromBeta(pRho.betaVec());
    Vector3 axisRho = boostRho.transform(ppim).p3().unit();
    _h[2]->fill(axisRho.dot(pRho.p3().unit()));
    LorentzTransform boostW = LorentzTransform::mkFrameTransformFromBeta(qq.betaVec());
    Vector3 axisE = boostW.transform(pe).p3().unit();
    _h[3]->fill(axisE.dot(qq.p3().unit()));
    axisRho.setZ(0.);
    axisE.setZ(0.);
    double chi = atan2(axisE.cross(axisRho).dot(qq.p3().unit()), axisE.dot(axisRho));
    _h[4]->fill(chi);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1., false);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2024_I2825816);

} ```