Rivet analyses

Mass distributions in J/ψ → γπ+π− and J/ψ → γπ0π0

Experiment: BESII (BEPC)

Inspire ID: 712991

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 642 (2006) 441-448

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi, originally e+e-

Measurement of the pion pair mass distribution in J/ψ → γπ+π− and J/ψ → γπ0π0. The data were read from the plots in the paper and the backgrounds given subtracted.

Source code:BESII_2006_I712991.cc

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

namespace Rivet {


  /// @brief J/psi -> gamma pi pi
  class BESII_2006_I712991 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESII_2006_I712991);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 443);
      declare(ufs, "UFS");
      DecayedParticles PSI(ufs);
      PSI.addStable(PID::ETA);
      PSI.addStable(PID::PI0);
      declare(PSI, "PSI");
      // histos
      for (unsigned int ix = 0; ix < 2; ++ix) {
        book(_h[ix], 1 + ix, 1, 1);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // find the J/psi decays
      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
      // loop over particles
      for (unsigned int ix = 0; ix < PSI.decaying().size(); ++ix) {
        unsigned int imode = 0;
        if (PSI.modeMatches(ix, 3, mode1))
          imode = 0;
        else if (PSI.modeMatches(ix, 3, mode2))
          imode = 1;
        else
          continue;
        const Particle& gam = PSI.decayProducts()[0].at(22)[0];
        _h[imode]->fill((PSI.decaying()[ix].mom() - gam.mom()).mass());
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h, 1.0, false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2];
    const map<PdgId, unsigned int> mode1 = {{211, 1}, {-211, 1}, {22, 1}};
    const map<PdgId, unsigned int> mode2 = {{111, 2}, {22, 1}};
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESII_2006_I712991);

}