Rivet analyses

Mass distributions in the decay ϕ → π+π−π0

Experiment: SND (VEPP-2M)

Inspire ID: 558279

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D65 (2002) 032002

Beams: * *

Beam energies: ANY

Run details: - Any process producing the decay

Measurement of the π + π− and π±π0 mass distributions in the decay ϕ → π+π−π0 by the SND experiment.

Source code:SND_2001_I558279.cc

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

namespace Rivet {


  /// @brief phi -> 3 pion decay
  class SND_2001_I558279 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2001_I558279);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(), "UFS");
      // Book histograms
      book(_h_pm, 1, 1, 1);
      book(_h_p0, 2, 1, 1);
    }

    void findDecayProducts(const Particle& mother,
                           unsigned int& nstable,
                           Particles& pip,
                           Particles& pim,
                           Particles& pi0) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (id == PID::PIMINUS) {
          pim.push_back(p);
          ++nstable;
        }
        else if (id == PID::PIPLUS) {
          pip.push_back(p);
          ++nstable;
        }
        else if (id == PID::PI0) {
          pi0.push_back(p);
          ++nstable;
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nstable, pip, pim, pi0);
        }
        else
          ++nstable;
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == 333)) {
        Particles pip, pim, pi0;
        unsigned int nstable(0);
        findDecayProducts(p, nstable, pip, pim, pi0);
        if (nstable == 3 && pip.size() == 1 && pim.size() == 1 && pi0.size() == 1) {
          _h_pm->fill((pip[0].momentum() + pim[0].momentum()).mass() / MeV);
          _h_p0->fill((pip[0].momentum() + pi0[0].momentum()).mass() / MeV);
          _h_p0->fill((pim[0].momentum() + pi0[0].momentum()).mass() / MeV);
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {

      normalize(_h_pm);
      normalize(_h_p0);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_pm, _h_p0;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(SND_2001_I558279);


}