Rivet analyses

title: BESIII_2024_I2730532

Mass distributions for $D^0\to2\pi^+2\pi^-$ and $\pi^+\pi^-2\pi^0$

Experiment: BESIII (BEPC)

Inspire ID: 2730532

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 1605.03814'

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0 mesons, originally e+e-

Mass distributions for $D^0\to2\pi^+2\pi^-$ and $\pi^+\pi^-2\pi^0$.

Source code:BESIII_2024_I2730532.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D0 -> 4 pions class BESIII_2024_I2730532 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2730532);

/// @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");
  for (unsigned int ix = 0; ix < 7; ++ix) {
    book(_h_0[ix], 2, 1, 1 + ix);
    if (ix >= 3) continue;
    book(_h_c[ix], 1, 1, 1 + ix);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // define the decay mode
  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;
    if (D0.modeMatches(ix, 4, mode1)) {
      const Particles& pip = D0.decayProducts()[ix].at(sign * 211);
      const Particles& pim = D0.decayProducts()[ix].at(-sign * 211);
      bool Kveto = false;
      set<double> mpm;
      for (unsigned int ix = 0; ix < 2; ++ix) {
        if ((pim[0].mom() + pim[1].mom() + pip[ix].mom()).mass() < 0.51) continue;
        for (unsigned int iy = 0; iy < 2; ++iy) {
          double m = (pip[ix].mom() + pim[iy].mom()).mass();
          mpm.insert(m);
          if (abs(m - .4976) < 0.03) Kveto = true;
        }
      }
      if (Kveto) continue;
      for (const double& m : mpm) _h_c[0]->fill(m);
      for (unsigned int ix = 0; ix < 2; ++ix) {
        _h_c[1]->fill((D0.decaying()[ix].mom() - pim[ix].mom()).mass());
        _h_c[2]->fill((D0.decaying()[ix].mom() - pip[ix].mom()).mass());
      }
    }
    else if (D0.modeMatches(ix, 4, mode2)) {
      const Particles& pi0 = D0.decayProducts()[ix].at(111);
      const Particle& pip = D0.decayProducts()[ix].at(sign * 211)[0];
      const Particle& pim = D0.decayProducts()[ix].at(-sign * 211)[0];
      double m00 = (pi0[0].mom() + pi0[1].mom()).mass();
      if (m00 > 0.4376 && m00 < 5276) continue;
      double mpm = (pip.mom() + pim.mom()).mass();
      if (abs(mpm - .4976) < 0.03) continue;
      double mp0[2], mm0[2], mpm0[2];
      bool veto = false;
      for (unsigned int ix = 0; ix < 2; ++ix) {
        mp0[ix] = (pi0[ix].mom() + pip.mom()).mass();
        mm0[ix] = (pi0[ix].mom() + pim.mom()).mass();
        if (mm0[ix] > 0.4677 && mm0[ix] < .5067) veto = true;
        mpm0[ix] = (pi0[ix].mom() + pim.mom() + pip.mom()).mass();
        if (mpm0[ix] < .57) veto = true;
      }
      if (veto) continue;
      for (unsigned int ix = 0; ix < 2; ++ix) {
        _h_0[0]->fill(mpm0[ix]);
        _h_0[5]->fill(mp0[ix]);
        _h_0[6]->fill(mm0[ix]);
      }
      _h_0[1]->fill((pi0[0].mom() + pi0[1].mom() + pip.mom()).mass());
      _h_0[2]->fill((pi0[0].mom() + pi0[1].mom() + pim.mom()).mass());
      _h_0[3]->fill(mpm);
      _h_0[4]->fill(m00);
    }
  }
}

/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_c);
  normalize(_h_0);
}
/// @}

/// @name Histograms
/// @{
Histo1DPtr _h_c[3], _h_0[7];
const map<PdgId, unsigned int> mode1 = {{211, 2}, {-211, 2}};
const map<PdgId, unsigned int> mode2 = {{111, 2}, {211, 1}, {-211, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2024_I2730532);

} ```