Rivet analyses

title: BESIII_2022_I2167804

$\psi(2S)\to \Lambda \bar{\Lambda}\eta$

Experiment: BESIII (BEPC)

Inspire ID: 2167804

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2207.14350

Beams: * *

Beam energies: ANY

Run details: - Any process producing psi(2S) originally e+e-

Measurement of the mass distributions in the decay $\psi(2S)\to \Lambda \bar{\Lambda}\eta$. The data were read from the plots in the paper. It is also not clear that any resolution effects have been unfolded.

Source code:BESIII_2022_I2167804.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief psi(2S) -> Lambda Lambdabar eta class BESIII_2022_I2167804 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2167804);


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

/// Book histograms and initialise projections before the run
void init() {
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 100443);
  declare(ufs, "UFS");
  DecayedParticles psi(ufs);
  psi.addStable(PID::PI0);
  psi.addStable(PID::K0S);
  psi.addStable(PID::ETA);
  psi.addStable(PID::ETAPRIME);
  psi.addStable(PID::OMEGA);
  psi.addStable(3122);
  psi.addStable(-3122);
  declare(psi, "psi");
  for (unsigned int ix = 0; ix < 3; ++ix) book(_h[ix], 1, 1, 1 + ix);
  book(_dalitz, "dalitz", 50, 2., 7., 50, 2., 7.);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{3122, 1}, {-3122, 1}, {221, 1}};
  DecayedParticles psi = apply<DecayedParticles>(event, "psi");
  // loop over particles
  for (unsigned int ix = 0; ix < psi.decaying().size(); ++ix) {
    if (!psi.modeMatches(ix, 3, mode)) continue;
    const Particle& eta = psi.decayProducts()[ix].at(221)[0];
    const Particle& lam = psi.decayProducts()[ix].at(3122)[0];
    const Particle& lbar = psi.decayProducts()[ix].at(-3122)[0];
    double mminus = (lbar.momentum() + eta.momentum()).mass2();
    double mplus = (lam.momentum() + eta.momentum()).mass2();
    _h[0]->fill(sqrt(mplus));
    _h[1]->fill(sqrt(mminus));
    _h[2]->fill((lam.momentum() + lbar.momentum()).mass());
    _dalitz->fill(mplus, mminus);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 3; ++ix) normalize(_h[ix], 1., false);
  normalize(_dalitz);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[3];
Histo2DPtr _dalitz;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2022_I2167804);

} ```