Rivet analyses

Mass spectrum of ηπ in ϕ → ηπ0γ decays

Experiment: SND (VEPP-2M)

Inspire ID: 525398

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B479 (2000) 53-58

Beams: * *

Beam energies: ANY

Run details: - Any process producing phi mesons

Mass spectra for ηπ in ϕ decays to ηπ0γ measured by KLOE. Useful for teting the treatment of the a_0(980) meson.

Source code:SND_2000_I525398.cc

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

namespace Rivet {


  /// @brief phi -> eta pi0 gamma
  class SND_2000_I525398 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2000_I525398);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(UnstableParticles(), "UFS");
      book(_h_etapi, 1, 1, 1);
      book(_nPhi, "TMP/nPhi");
    }

    void findDecayProducts(const Particle& mother,
                           unsigned int& nstable,
                           unsigned int& neta,
                           unsigned int& npi,
                           unsigned int& ngamma,
                           FourMomentum& ptot) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (id == PID::ETA) {
          ++neta;
          ++nstable;
          ptot += p.momentum();
        }
        else if (id == PID::PI0) {
          ++npi;
          ++nstable;
          ptot += p.momentum();
        }
        else if (id == PID::GAMMA) {
          ++ngamma;
          ++nstable;
        }
        else if (id == PID::PIPLUS || id == PID::PIMINUS) {
          ++nstable;
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nstable, neta, npi, ngamma, ptot);
        }
        else
          ++nstable;
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {

      // Loop over phis
      for (const Particle& phi : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == PID::PHI)) {
        _nPhi->fill();
        unsigned int nstable(0), neta(0), npi(0), ngamma(0);
        FourMomentum p_tot(0, 0, 0, 0);
        findDecayProducts(phi, nstable, neta, npi, ngamma, p_tot);
        if (nstable != 3) continue;
        if (neta == 1 && npi == 1 && ngamma == 1) {
          _h_etapi->fill(p_tot.mass() / MeV);
        }
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      // normalise to total no of phi mesons
      scale(_h_etapi, 1. / *_nPhi);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_etapi;
    CounterPtr _nPhi;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(SND_2000_I525398);


}