Rivet analyses

title: BES_1999_I498114

Hadronic Mass in $J/\psi\to\gamma \eta\pi^+\pi^-$

Experiment: BES (BEPC)

Inspire ID: 498114

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 446 (1999) 356-362

Beams: * *

Beam energies: ANY

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

Measurement of the hadronic mass in $J/\psi\to\gamma \eta\pi^+\pi^-$. The data were read from figure 2 in the paper and the background given subtracted.

Source code:BES_1999_I498114.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> gamma eta pi+ pi- class BES_1999_I498114 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BES_1999_I498114);


/// @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);
  declare(PSI, "PSI");
  // histos
  book(_h, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // find the J/psi decays
  static const map<PdgId, unsigned int>& mode = {{221, 1}, {211, 1}, {211, 1}, {22, 1}};
  DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
  // loop over particles
  for (unsigned int ix = 0; ix < PSI.decaying().size(); ++ix) {
    if (!PSI.modeMatches(ix, 4, mode)) continue;
    const Particle& gam = PSI.decayProducts()[0].at(22)[0];
    _h->fill((PSI.decaying()[ix].mom() - gam.mom()).mass());
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
/// @}

};

RIVET_DECLARE_PLUGIN(BES_1999_I498114);

} ```