Rivet analyses

title: BESIII_2021_I1870388

$\chi_{c(0,1,2)}\to n K^0_S\bar{\Lambda}^0$ + c.c

Experiment: BESIII (BEPC)

Inspire ID: 1870388

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - JHEP 11 (2021) 217

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_c originally e+e-

Measurement of the mass distributions in the decays $\chi_{c(0,1,2)}\to n K^0_S\bar{\Lambda}^0$ + c.c. The data were read from the plots in the paper and may not be corrected for efficiency or background.

Source code:BESIII_2021_I1870388.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief chi_c -> n K0S Lambdabar +cc class BESIII_2021_I1870388 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1870388);


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

/// Book histograms and initialise projections before the run
void init() {
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 20443 or Cuts::pid == 445 or Cuts::pid == 10441);
  declare(ufs, "UFS");
  DecayedParticles chi(ufs);
  chi.addStable(PID::PI0);
  chi.addStable(PID::K0S);
  chi.addStable(PID::ETA);
  chi.addStable(PID::ETAPRIME);
  chi.addStable(PID::LAMBDA);
  chi.addStable(-PID::LAMBDA);
  declare(chi, "chi");
  // histograms
  for (unsigned int ix = 0; ix < 3; ++ix) {
    book(_dalitz[ix], "dalitz_" + toString(ix + 1), 50, 2., 7., 50, 2., 6.2);
    for (unsigned int iy = 0; iy < 3; ++iy) book(_h[ix][iy], ix + 1, 1, iy + 1);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{2112, 1}, {-3122, 1}, {310, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-2112, 1}, {3122, 1}, {310, 1}};
  DecayedParticles chi = apply<DecayedParticles>(event, "chi");
  // loop over particles
  for (unsigned int ix = 0; ix < chi.decaying().size(); ++ix) {
    int sign = 1;
    if (chi.modeMatches(ix, 3, mode)) {
      sign = 1;
    }
    else if (chi.modeMatches(ix, 3, modeCC)) {
      sign = -1;
    }
    else
      continue;
    unsigned int iloc = chi.decaying()[ix].pid() == 10441 ? 0 : chi.decaying()[ix].pid() == 445 ? 2 : 1;
    const Particle& KS0 = chi.decayProducts()[ix].at(310)[0];
    const Particle& nn = chi.decayProducts()[ix].at(sign * 2112)[0];
    const Particle& lbar = chi.decayProducts()[ix].at(-sign * 3122)[0];
    double mnLam = (nn.momentum() + lbar.momentum()).mass2();
    double mnK = (nn.momentum() + KS0.momentum()).mass2();
    double mKLam = (lbar.momentum() + KS0.momentum()).mass2();
    _h[iloc][0]->fill(sqrt(mnLam));
    _h[iloc][1]->fill(sqrt(mnK));
    _h[iloc][2]->fill(sqrt(mKLam));
    _dalitz[iloc]->fill(mKLam, mnK);
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2021_I1870388);

} ```