Rivet analyses

title: BESIII_2024_I2801948

Mass distributions in $D_s^+\to \pi^+\pi^+\pi^-\pi^0$ decays

Experiment: BESIII (BEPC)

Inspire ID: 2801948

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 134 (2025) 1, 011904 - arXiv: 2406.17452

Beams: * *

Beam energies: ANY

Run details: - Any process producting D_s mesons, originally e+e-

Measurement of the mass distributions in the decay $D_s^+\to \pi^+\pi^+\pi^-\pi^0$. The data were read from the plots in the paper. Resolution/acceptance effects have been not unfolded and given the agreement with the model in the paper this analysis should only be used for qualitative studies.

Source code:BESIII_2024_I2801948.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D_s+ -> pi+ pi+ pi- pi0 class BESIII_2024_I2801948 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2801948);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 431);
  declare(ufs, "UFS");
  DecayedParticles DS(ufs);
  DS.addStable(PID::PI0);
  DS.addStable(PID::K0S);
  declare(DS, "DS");
  // histos
  for (unsigned int ix = 0; ix < 7; ++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 = {{211, 2}, {-211, 1}, {111, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-211, 2}, {211, 1}, {111, 1}};
  DecayedParticles DS = apply<DecayedParticles>(event, "DS");
  // loop over particles
  for (unsigned int ix = 0; ix < DS.decaying().size(); ++ix) {
    int sign = 1;
    if (DS.decaying()[ix].pid() > 0 && DS.modeMatches(ix, 4, mode)) {
      sign = 1;
    }
    else if (DS.decaying()[ix].pid() < 0 && DS.modeMatches(ix, 4, modeCC)) {
      sign = -1;
    }
    else
      continue;
    const Particle& pi0 = DS.decayProducts()[ix].at(111)[0];
    const Particles& pip = DS.decayProducts()[ix].at(sign * 211);
    const Particle& pim = DS.decayProducts()[ix].at(-sign * 211)[0];
    double mpm[2];
    bool veto = false;
    for (unsigned int ix = 0; ix < 2; ++ix) {
      mpm[ix] = (pip[ix].momentum() + pim.momentum()).mass();
      if (mpm[ix] > 0.46 && mpm[ix] < 0.52) veto = true;
    }
    if (veto) continue;
    // eta veto
    double mpm0[2];
    for (unsigned int ix = 0; ix < 2; ++ix) {
      mpm0[ix] = (pip[ix].momentum() + pim.momentum() + pi0.momentum()).mass();
      if (mpm0[ix] > 0.52 && mpm0[ix] < 0.58) veto = true;
    }
    if (veto) continue;
    _h[0]->fill((pip[0].momentum() + pip[1].momentum()).mass());
    _h[1]->fill((pim.momentum() + pi0.momentum()).mass());
    _h[4]->fill((pip[0].momentum() + pip[1].momentum() + pim.momentum()).mass());
    _h[5]->fill((pip[0].momentum() + pip[1].momentum() + pi0.momentum()).mass());
    for (unsigned int ix = 0; ix < 2; ++ix) {
      _h[2]->fill(mpm[ix]);
      _h[3]->fill((pip[ix].momentum() + pi0.momentum()).mass());
      _h[6]->fill(mpm0[ix]);
    }
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[7];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2024_I2801948);

} ```