Rivet analyses

η′ → π+π−γ decays

Experiment: BESIII (BEPC)

Inspire ID: 1641075

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 120 (2018) 242003, 2018

Beams: * *

Beam energies: ANY

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

Differential decay rates for η′ → π+π−γ decays. Data from HEPData has been manipulated to remove the background, correct for the efficiency, and normalise the distribution.

Source code:BESIII_2018_I1641075.cc

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

namespace Rivet {


  /// @brief eta' -> pi+pi- gamma decay
  class BESIII_2018_I1641075 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1641075);


    /// @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);
      ETA.addStable(PID::PI0);
      declare(ETA, "ETA");

      // Book histograms
      book(_h_m, 1, 1, 5);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{PID::PIPLUS, 1}, {PID::PIMINUS, 1}, {PID::GAMMA, 1}};
      DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
      // loop over particles
      for (unsigned int ix = 0; ix < ETA.decaying().size(); ++ix) {
        if (!ETA.modeMatches(ix, 3, mode)) continue;
        const Particle& pip = ETA.decayProducts()[ix].at(PID::PIPLUS)[0];
        const Particle& pim = ETA.decayProducts()[ix].at(PID::PIMINUS)[0];
        _h_m->fill((pip.momentum() + pim.momentum()).mass());
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_m;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2018_I1641075);


}