Rivet analyses

title: SND_2001_I558279

Mass distributions in the decay $\phi\to\pi^+\pi^-\pi^0$

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 $\pi+\pi^-$ and $\pi^\pm\pi^0$ mass distributions in the decay $\phi\to\pi^+\pi^-\pi^0$ by the SND experiment.

Source code:SND_2001_I558279.cc

```c++ // -- 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);

} ```