Rivet analyses

title: BESII_2006_I712991

Mass distributions in $J/\psi\to\gamma\pi^+\pi^-$ and $J/\psi\to\gamma\pi^0\pi^0$

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 $J/\psi\to\gamma\pi^+\pi^-$ and $J/\psi\to\gamma\pi^0\pi^0$. The data were read from the plots in the paper and the backgrounds given subtracted.

Source code:BESII_2006_I712991.cc

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

} ```