Rivet analyses

title: BESIII_2021_I1929365

Dalitz plot analysis of $D_s^+\to \pi^+\pi^0\pi^0$

Experiment: BESIII (BEPC)

Inspire ID: 1929365

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - JHEP 01 (2022) 052

Beams: * *

Beam energies: ANY

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

Measurement of the mass distributions in the decay $D_s^+\to \pi^+\pi^0\pi^0$. 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_2021_I1929365.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D_s+ -> pi+ pi0 pi0 class BESIII_2021_I1929365 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1929365);


/// @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
  book(_h_pi0pi0, 1, 1, 1);
  book(_h_pippi0, 1, 1, 2);
  book(_dalitz, "dalitz", 50, 0., 3.5, 50, 0., 3.5);
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{211, 1}, {111, 2}};
  static const map<PdgId, unsigned int>& modeCC = {{-211, 1}, {111, 2}};
  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, 3, mode)) {
      sign = 1;
    }
    else if (DS.decaying()[ix].pid() < 0 && DS.modeMatches(ix, 3, modeCC)) {
      sign = -1;
    }
    else
      continue;
    const Particles& pi0 = DS.decayProducts()[ix].at(111);
    const Particle& pip = DS.decayProducts()[ix].at(sign * 211)[0];
    double mp1 = (pip.momentum() + pi0[0].momentum()).mass2();
    double mp2 = (pip.momentum() + pi0[1].momentum()).mass2();
    double m0 = (pi0[0].momentum() + pi0[1].momentum()).mass();
    _dalitz->fill(mp1, mp2);
    _dalitz->fill(mp2, mp1);
    // K_S0 veto
    if (m0 > 0.458 && m0 < 0.520) continue;
    _h_pippi0->fill(sqrt(mp1));
    _h_pippi0->fill(sqrt(mp2));
    _h_pi0pi0->fill(m0);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_pi0pi0);
  normalize(_h_pippi0);
  normalize(_dalitz);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_pi0pi0, _h_pippi0;
Histo2DPtr _dalitz;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2021_I1929365);

} ```