Rivet analyses

title: BES_1999_I507639

Hadronic mass distribution in $J/\psi\to\gamma \pi^+\pi^-\pi^+\pi^-$

Experiment: BES (BEPC)

Inspire ID: 507639

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 472 (2000) 207-214

Beams: * *

Beam energies: ANY

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

Hadronic mass distribution in $J/\psi\to\gamma \pi^+\pi^-\pi^+\pi^-$. Only the $\pi^+\pi^-\pi^+\pi^-$ mass distribution isa implemented as the background is not given for the other distributions. The data were read from figure 4d and the background given subtracted.

Source code:BES_1999_I507639.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> gamma 2pi+ 2pi- class BES_1999_I507639 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BES_1999_I507639);


/// @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::K0S);
  PSI.addStable(PID::PI0);
  declare(PSI, "PSI");
  // histos
  book(_h, 1, 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) {
    if (!PSI.modeMatches(ix, 5, mode)) continue;
    const Particles& pip = PSI.decayProducts()[0].at(211);
    const Particles& pim = PSI.decayProducts()[0].at(-211);
    FourMomentum ptotal;
    for (unsigned int iy = 0; iy < 2; ++iy) {
      ptotal += pip[ix].momentum() + pim[ix].momentum();
    }
    _h->fill(ptotal.mass());
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
const map<PdgId, unsigned int> mode = {{211, 2}, {-211, 2}, {22, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BES_1999_I507639);

} ```