Rivet analyses

title: BESIII_2017_I1490896

$\chi_{c1}\to \eta\pi^+\pi^-$

Experiment: BESIII (BEPC)

Inspire ID: 1490896

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 95 (2017) 3, 032002

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_c1

Measurement of the mass distributions in the decays $\chi_{c1}\to \eta\pi^+\pi^-$. The data were read from the plots in the paper and may not be corrected for efficiency.

Source code:BESIII_2017_I1490896.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief chi_c1 -> eta pi+pi- class BESIII_2017_I1490896 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1490896);


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

/// Book histograms and initialise projections before the run
void init() {
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 20443);
  declare(ufs, "UFS");
  DecayedParticles chi(ufs);
  chi.addStable(PID::PI0);
  chi.addStable(PID::K0S);
  chi.addStable(PID::ETA);
  declare(chi, "chi");
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, ix + 1);
  book(_dalitz, "dalitz", 50, 0., 12., 50, 0., 9.);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode1 = {{221, 1}, {211, 1}, {-211, 1}};
  DecayedParticles chi = apply<DecayedParticles>(event, "chi");
  // loop over particles
  for (unsigned int ix = 0; ix < chi.decaying().size(); ++ix) {
    if (chi.modeMatches(ix, 3, mode1)) {
      const Particle& eta = chi.decayProducts()[ix].at(221)[0];
      const Particle& pim = chi.decayProducts()[ix].at(-211)[0];
      const Particle& pip = chi.decayProducts()[ix].at(211)[0];
      double m1 = (pip.momentum() + pim.momentum()).mass2();
      double m2 = (eta.momentum() + pip.momentum()).mass2();
      double m3 = (eta.momentum() + pim.momentum()).mass2();
      _dalitz->fill(m2, m1);
      _h[1]->fill(sqrt(m1));
      _h[0]->fill(sqrt(m2));
      _h[0]->fill(sqrt(m3));
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_dalitz);
  for (unsigned int iy = 0; iy < 2; ++iy) normalize(_h[iy]);
}
/// @}

/// @name Histograms
/// @{
Histo1DPtr _h[2];
Histo2DPtr _dalitz;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2017_I1490896);

} ```