Rivet analyses

Kinematic distributions in the decays η′ → π+π−π0 and ππ0π0

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 η′ → ηπ0π0. Data was read from the graphs and the simulated background from the plots subtracted.

Source code:BESIII_2017_I1469067.cc

// -*- 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);

}