Rivet analyses

title: BESIII_2025_I2866208

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

Experiment: BESIII (BESIII)

Inspire ID: 2866208

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2501.04451

Beams: * *

Beam energies: ANY

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

Measurement of the mass distributions in the decay $D_s^+\to \pi^+\pi^+\pi^-\pi^0\pi^0$. 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_2025_I2866208.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 pi0 class BESIII_2025_I2866208 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2025_I2866208);


/// @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 (size_t ix = 0; ix < 8; ++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, 2}};
  static const map<PdgId, unsigned int>& modeCC = {{-211, 2}, {211, 1}, {111, 2}};
  DecayedParticles DS = apply<DecayedParticles>(event, "DS");
  // loop over particles
  for (size_t id = 0; id < DS.decaying().size(); ++id) {
    int sign = 1;
    if (DS.decaying()[id].pid() > 0 && DS.modeMatches(id, 5, mode)) {
      sign = 1;
    }
    else if (DS.decaying()[id].pid() < 0 && DS.modeMatches(id, 5, modeCC)) {
      sign = -1;
    }
    else
      continue;
    const Particles& pi0 = DS.decayProducts()[id].at(111);
    const Particles& pip = DS.decayProducts()[id].at(sign * 211);
    const Particle& pim = DS.decayProducts()[id].at(-sign * 211)[0];
    double m0 = (pi0[0].mom() + pi0[1].mom()).mass();
    // K_S0 veto
    if (m0 > 0.487 && m0 < 0.511) continue;
    if (pip[0].parents()[0].pid() == PID::K0S || pip[1].parents()[0].pid() == PID::K0S
        || pim.parents()[0].pid() == PID::K0S)
      continue;
    // eta veto
    double mpm0[4];
    bool passCut = true;
    for (size_t ix = 0; ix < 2; ++ix) {
      for (size_t iy = 0; iy < 2; ++iy) {
        mpm0[2 * ix + iy] = (pi0[ix].mom() + pip[iy].mom() + pim.mom()).mass();
        if (mpm0[2 * ix + iy] > .49 && mpm0[2 * ix + iy] < .58) passCut = false;
      }
    }
    if (!passCut) continue;
    _h[0]->fill(m0);
    for (size_t ix = 0; ix < 4; ++ix) {
      _h[4]->fill(mpm0[ix] / GeV);
    }
    _h[5]->fill((pi0[0].mom() + pi0[1].mom() + pim.mom()).mass() / GeV);
    for (size_t ix = 0; ix < 2; ++ix) {
      _h[2]->fill((pip[ix].mom() + pim.mom()).mass() / GeV);
      _h[3]->fill((pi0[ix].mom() + pim.mom()).mass() / GeV);
      _h[6]->fill((pip[0].mom() + pip[1].mom() + pi0[ix].mom() + pim.mom()).mass() / GeV);
      _h[7]->fill((pi0[0].mom() + pi0[1].mom() + pip[ix].mom() + pim.mom()).mass() / GeV);
      for (size_t iy = 0; iy < 2; ++iy) {
        _h[1]->fill((pip[ix].mom() + pi0[iy].mom()).mass() / GeV);
      }
    }
  }
}


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

/// @}

/// @name Histograms
/// @{
Histo1DPtr _h[8];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2025_I2866208); } ```