Rivet analyses

η′ → π+π−e+e− decays

Experiment: BESIII (BEPC)

Inspire ID: 1830421

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 103 (2021) 9, 092005

Beams: * *

Beam energies: ANY

Run details: - Events with eta prime decays, either particle guns or collisions.

Differential decay rates for η′ → π+π−e+e− decays. Due to the resolution and backgrounds only the pion pair mass is used. The data were read from the plots in the paper.

Source code:BESIII_2020_I1830421.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief eta' -> pi+pi- e+e- decay
  class BESIII_2020_I1830421 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1830421);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 331);
      declare(ufs, "UFS");
      DecayedParticles ETA(ufs);
      declare(ETA, "ETA");
      // Book histograms
      //book(_h_mee  , 1, 1, 1);
      book(_h_mpipi, 1, 1, 2);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{211, 1}, {-211, 1}, {11, 1}, {-11, 1}};
      DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
      // loop over particles
      for (unsigned int ix = 0; ix < ETA.decaying().size(); ++ix) {
        if (!ETA.modeMatches(ix, 4, mode)) continue;
        const Particle& pip = ETA.decayProducts()[ix].at(211)[0];
        const Particle& pim = ETA.decayProducts()[ix].at(-211)[0];
        //const Particle & ep  = ETA.decayProducts()[ix].at(  11)[0];
        //const Particle & em  = ETA.decayProducts()[ix].at(- 11)[0];
        //_h_mee  ->fill((em .momentum()+ep .momentum()).mass());
        _h_mpipi->fill((pim.momentum() + pip.momentum()).mass());
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    //Histo1DPtr _h_mee;
    Histo1DPtr _h_mpipi;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2020_I1830421);

}