Rivet analyses

title: BESIII_2012_I1187787

Dalitz plot analysis of $\eta_c\to K^0_SK^\pm\pi^\mp$

Experiment: BESIII (BEPC)

Inspire ID: 1187787

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 86 (2012) 092009

Beams: * *

Beam energies: ANY

Run details: - Any process producing eta_c (originally psi(2S) -> gamma eta_c)

Measurement of the mass distributions in the decays $\eta_c\to K^0_SK^\pm\pi^\mp$ by BESIII. The data were read from the plots in the paper and therefore for some points the error bars are the size of the point. It is also not clear that any resolution effects have been unfolded.

Source code:BESIII_2012_I1187787.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief eta_c -> KS0 K+-pi-+ class BESIII_2012_I1187787 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2012_I1187787);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 441);
  declare(ufs, "UFS");
  DecayedParticles etac(ufs);
  etac.addStable(PID::PI0);
  etac.addStable(PID::K0S);
  etac.addStable(PID::ETA);
  etac.addStable(PID::ETAPRIME);
  declare(etac, "etac");
  // histograms
  book(_h_K0pip, 1, 1, 1);
  book(_h_K0Kp, 1, 1, 2);
  book(_h_Kppip, 1, 1, 3);
  book(_dalitz, "dalitz", 50, 0., 8., 50, 0., 8.);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{321, 1}, {310, 1}, {-211, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-321, 1}, {310, 1}, {211, 1}};
  DecayedParticles etac = apply<DecayedParticles>(event, "etac");
  // loop over particles
  for (unsigned int ix = 0; ix < etac.decaying().size(); ++ix) {
    int sign = 1;
    if (etac.modeMatches(ix, 3, mode)) {
      sign = 1;
    }
    else if (etac.modeMatches(ix, 3, modeCC)) {
      sign = -1;
    }
    else
      continue;
    const Particle& KS0 = etac.decayProducts()[ix].at(310)[0];
    const Particle& pim = etac.decayProducts()[ix].at(-sign * 211)[0];
    const Particle& Kp = etac.decayProducts()[ix].at(sign * 321)[0];
    double mplus = (Kp.momentum() + pim.momentum()).mass2();
    double mminus = (KS0.momentum() + pim.momentum()).mass2();
    double mKK = (Kp.momentum() + KS0.momentum()).mass2();
    _h_K0Kp->fill(sqrt(mKK));
    _h_Kppip->fill(sqrt(mplus));
    _h_K0pip->fill(sqrt(mminus));
    _dalitz->fill(mplus, mminus);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_Kppip);
  normalize(_h_K0pip);
  normalize(_h_K0Kp);
  normalize(_dalitz);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_Kppip, _h_K0pip, _h_K0Kp;
Histo2DPtr _dalitz;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2012_I1187787);

} ```