Rivet analyses

title: BESIII_2021_I1837968

Mass distributions in $\Lambda_c^+\to p K^0_S \eta$

Experiment: BESIII (BEPC)

Inspire ID: 1837968

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 817 (2021) 136327

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c+ mesons

Measurement of the mass distributions in the decay $\Lambda_c^+\to p K^0_S \eta$ by BESIII. The data were read from the plots in the paper and may not have been corrected for efficiency/acceptance.

Source code:BESIII_2021_I1837968.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Lambda_c+ -> p K0S eta class BESIII_2021_I1837968 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1837968);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 4122);
  declare(ufs, "UFS");
  DecayedParticles LAMBDAC(ufs);
  LAMBDAC.addStable(PID::PI0);
  LAMBDAC.addStable(PID::K0S);
  LAMBDAC.addStable(PID::ETA);
  declare(LAMBDAC, "LAMBDAC");
  // histograms
  for (unsigned int ix = 0; ix < 3; ++ix) book(_h[ix], 1, 1, 1 + ix);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{PID::PROTON, 1}, {310, 1}, {221, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-PID::PROTON, 1}, {310, 1}, {221, 1}};
  DecayedParticles LAMBDAC = apply<DecayedParticles>(event, "LAMBDAC");
  // loop over particles
  for (unsigned int ix = 0; ix < LAMBDAC.decaying().size(); ++ix) {
    int sign = 1;
    if (LAMBDAC.decaying()[ix].pid() > 0 && LAMBDAC.modeMatches(ix, 3, mode)) {
      sign = 1;
    }
    else if (LAMBDAC.decaying()[ix].pid() < 0 && LAMBDAC.modeMatches(ix, 3, modeCC)) {
      sign = -1;
    }
    else
      continue;
    const Particle& pp = LAMBDAC.decayProducts()[ix].at(sign * PID::PROTON)[0];
    const Particle& eta = LAMBDAC.decayProducts()[ix].at(221)[0];
    const Particle& K0 = LAMBDAC.decayProducts()[ix].at(310)[0];
    _h[0]->fill((pp.momentum() + K0.momentum()).mass());
    _h[1]->fill((K0.momentum() + eta.momentum()).mass());
    _h[2]->fill((pp.momentum() + eta.momentum()).mass());
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2021_I1837968);

} ```