Rivet analyses

Mass distributions in ψ(2S) → π+π−π0

Experiment: BES (BEPC)

Inspire ID: 689969

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 619 (2005) 247-254

Beams: * *

Beam energies: ANY

Run details: - Any process producingpsi(2S), originally e+e-

Measurement of the ππ mass distribution in the decays ψ(2S) → π+π−π0 be BES. N.B. data read from plots and may not be corrected.

Source code:BES_2005_I689969.cc

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

namespace Rivet {


  /// @brief psi(2S) -> pi+pi-pi0
  class BES_2005_I689969 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BES_2005_I689969);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 100443);
      declare(ufs, "UFS");
      DecayedParticles psi2S(ufs);
      psi2S.addStable(PID::PI0);
      psi2S.addStable(PID::K0S);
      psi2S.addStable(PID::ETA);
      psi2S.addStable(PID::ETAPRIME);
      declare(psi2S, "psi2S");
      book(_h_pipi, 1, 1, 1);
      book(_dalitz, "dalitz", 50, 0., 14., 50, 0.0, 14.);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{211, 1}, {-211, 1}, {111, 1}};
      DecayedParticles psi2S = apply<DecayedParticles>(event, "psi2S");
      // loop over particles
      for (unsigned int ix = 0; ix < psi2S.decaying().size(); ++ix) {
        if (!psi2S.modeMatches(ix, 3, mode)) continue;
        const Particles& pi0 = psi2S.decayProducts()[ix].at(111);
        const Particles& pip = psi2S.decayProducts()[ix].at(211);
        const Particles& pim = psi2S.decayProducts()[ix].at(-211);
        double mminus = (pim[0].momentum() + pi0[0].momentum()).mass2();
        double mplus = (pip[0].momentum() + pi0[0].momentum()).mass2();
        double mneut = (pip[0].momentum() + pim[0].momentum()).mass2();
        _h_pipi->fill(sqrt(mneut));
        _h_pipi->fill(sqrt(mplus));
        _h_pipi->fill(sqrt(mminus));
        _dalitz->fill(mplus, mminus);
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_pipi;
    Histo2DPtr _dalitz;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BES_2005_I689969);

}