Rivet analyses

title: BESIII_2024_I2777242

Dalitz decays $D^0\to\pi^+\pi^-\eta$ and $D^+\to\pi^+\pi^0\eta$

Experiment: BESIII (BEPC)

Inspire ID: 2777242

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 110 (2024) 11, L111102 - arXiv: 2404.09219

Beams: * *

Beam energies: ANY

Run details: - Any process producing D+/D0 mesons

Measurement of the mass distributions in the decays $D^0\to\pi^+\pi^-\eta$ and $D^+\to\pi^+\pi^0\eta$ by the BESIII collaboration. The data were read from the plots in the paper and resolution/efficiency effects have not been unfolded.

Source code:BESIII_2024_I2777242.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D0 -> pi+pi0eta and D+ -> pi+pi-eta class BESIII_2024_I2777242 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2777242);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 411 || Cuts::abspid == 421);
  declare(ufs, "UFS");
  DecayedParticles DD(ufs);
  DD.addStable(PID::PI0);
  DD.addStable(PID::K0S);
  DD.addStable(PID::ETA);
  declare(DD, "DD");
  // // histograms
  for (unsigned int ix = 0; ix < 2; ++ix) {
    for (unsigned int iy = 0; iy < 2; ++iy) book(_h_etapi[ix][iy], 1, 1 + ix, 1 + iy);
    book(_h_pipi[ix], 1, 1 + ix, 3);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int> mode[2] = {{{211, 1}, {-211, 1}, {221, 1}},
                                                   {{211, 1}, {111, 1}, {221, 1}}};
  static const map<PdgId, unsigned int> modeCC[2] = {{{211, 1}, {-211, 1}, {221, 1}},
                                                     {{-211, 1}, {111, 1}, {221, 1}}};
  DecayedParticles DD = apply<DecayedParticles>(event, "DD");
  // loop over particles
  for (unsigned int ix = 0; ix < DD.decaying().size(); ++ix) {
    unsigned int ip = DD.decaying()[ix].abspid() == 411 ? 1 : 0;
    int sign = 1;
    if (DD.decaying()[ix].pid() > 0 && DD.modeMatches(ix, 3, mode[ip])) {
      sign = 1;
    }
    else if (DD.decaying()[ix].pid() < 0 && DD.modeMatches(ix, 3, modeCC[ip])) {
      sign = -1;
    }
    else
      continue;
    const Particle& eta = DD.decayProducts()[ix].at(221)[0];
    const Particle& pim = ip == 0 ? DD.decayProducts()[ix].at(-sign * 211)[0]
                                  : DD.decayProducts()[ix].at(111)[0];
    const Particle& pip = DD.decayProducts()[ix].at(sign * 211)[0];
    double mpipi = (pim.momentum() + pip.momentum()).mass();
    // apply KS0 cut
    if (ip == 0 && abs(mpipi - .497611) < 0.03) continue;
    // mass dists
    _h_pipi[ip]->fill(mpipi);
    _h_etapi[ip][0]->fill((eta.momentum() + pip.momentum()).mass());
    _h_etapi[ip][1]->fill((eta.momentum() + pim.momentum()).mass());
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_pipi);
  normalize(_h_etapi);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_pipi[2], _h_etapi[2][2];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2024_I2777242);

} ```