Rivet analyses

title: BESIII_2022_I2615968

Dalitz plot analysis of $D^0\to K^0_{S,L}\pi^+\pi^-$

Experiment: BESIII (BEPC)

Inspire ID: 2615968

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2212.09048

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0 mesons

Measurement of Kinematic distributions in the decay $D^0\to K^0_S\pi^+\pi^-$ by BESIII. The data were read from the plots in the paper and resolution/acceptance effects may not have been unfolded.

Source code:BESIII_2022_I2615968.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D0 -> KS0, KL0 pi+ pi- class BESIII_2022_I2615968 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2615968);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 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");
  // Histograms
  for (unsigned int ix = 0; ix < 2; ++ix)
    for (unsigned int iy = 0; iy < 3; ++iy) book(_h[ix][iy], 1 + ix, 1, 1 + iy);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // // define the decay mode
  static const map<PdgId, unsigned int>& mode1 = {{310, 1}, {211, 1}, {-211, 1}};
  static const map<PdgId, unsigned int>& mode2 = {{130, 1}, {211, 1}, {-211, 1}};
  DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
  // loop over particles
  for (unsigned int ix = 0; ix < D0.decaying().size(); ++ix) {
    int sign = D0.decaying()[ix].pid() / 421;
    int imode = 0;
    // KS0 pi+pi-
    if (D0.modeMatches(ix, 3, mode1))
      imode = 0;
    else if (D0.modeMatches(ix, 3, mode2))
      imode = 1;
    else
      continue;
    const Particle& pip = D0.decayProducts()[ix].at(sign * 211)[0];
    const Particle& pim = D0.decayProducts()[ix].at(-sign * 211)[0];
    const Particle& K0 = D0.decayProducts()[ix].at(imode == 0 ? 310 : 130)[0];
    double mminus = (pim.momentum() + K0.momentum()).mass2();
    double mplus = (pip.momentum() + K0.momentum()).mass2();
    double mpipi = (pip.momentum() + pim.momentum()).mass2();
    _h[imode][0]->fill(mplus);
    _h[imode][1]->fill(mminus);
    _h[imode][2]->fill(mpipi);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix)
    for (unsigned int iy = 0; iy < 3; ++iy) normalize(_h[ix][iy], 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2][3];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2022_I2615968);

} ```