Rivet analyses

title: BESIII_2017_I1469067

Kinematic distributions in the decays $\eta^\prime\to\pi^+\pi^-\pi^0$ and $\pi\pi^0\pi^0$

Experiment: BESIII (BEPC)

Inspire ID: 1469067

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 118 (2017) 1, 012001

Beams: * *

Beam energies: ANY

Run details: - Any process producing etaprime mesons

Measurement of kinematic distributions in the decay $\eta^\prime\to\eta\pi^0\pi^0$. Data was read from the graphs and the simulated background from the plots subtracted.

Source code:BESIII_2017_I1469067.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief eta' -> pions class BESIII_2017_I1469067 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1469067);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == PID::ETAPRIME);
  declare(ufs, "UFS");
  DecayedParticles ETA(ufs);
  ETA.addStable(PID::PI0);
  ETA.addStable(PID::K0S);
  ETA.addStable(PID::ETA);
  declare(ETA, "ETA");
  // histograms
  for (unsigned int ix = 0; ix < 4; ++ix) {
    book(_h[ix], 1, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode1 = {{211, 1}, {-211, 1}, {111, 1}};
  static const map<PdgId, unsigned int>& mode2 = {{111, 3}};
  DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
  // loop over particles
  for (unsigned int ix = 0; ix < ETA.decaying().size(); ++ix) {
    // select right decay mode
    if (ETA.modeMatches(ix, 3, mode1)) {
      const Particle& pi0 = ETA.decayProducts()[ix].at(111)[0];
      const Particle& pip = ETA.decayProducts()[ix].at(211)[0];
      const Particle& pim = ETA.decayProducts()[ix].at(-211)[0];
      _h[0]->fill((pip.momentum() + pim.momentum()).mass());
      _h[1]->fill((pip.momentum() + pi0.momentum()).mass());
      _h[2]->fill((pim.momentum() + pi0.momentum()).mass());
    }
    else if (ETA.modeMatches(ix, 3, mode2)) {
      const Particles& pi0 = ETA.decayProducts()[ix].at(111);
      for (unsigned int ix = 0; ix < 3; ++ix) {
        for (unsigned int iy = ix + 1; iy < 3; ++iy)
          _h[3]->fill((pi0[ix].momentum() + pi0[iy].momentum()).mass());
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // normalize the histograms
  for (unsigned int ix = 0; ix < 4; ++ix) normalize(_h[ix]);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[4];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2017_I1469067);

} ```