Rivet analyses

Mass distributions in Λc+ → Λπ+η

Experiment: BESIII (BEPC)

Inspire ID: 2808543

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 134 (2025) 2, 021901 - arXiv: 2407.12270

Beams: * *

Beam energies: ANY

Run details: none listed

Measurement of the mass distributions in the decay Λc+ → Λπ+η by BESIII. The data were read from the plots in the paper and may not have been corrected for efficiency/acceptance.

Source code:BESIII_2024_I2808543.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief Lambda_c+ -> Lambda pi+ eta
  class BESIII_2024_I2808543 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2808543);


    /// @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::ETA);
      LAMBDAC.addStable(PID::LAMBDA);
      LAMBDAC.addStable(-PID::LAMBDA);
      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::LAMBDA, 1}, {211, 1}, {221, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{-PID::LAMBDA, 1}, {-211, 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& lam = LAMBDAC.decayProducts()[ix].at(sign * PID::LAMBDA)[0];
        const Particle& eta = LAMBDAC.decayProducts()[ix].at(PID::ETA)[0];
        const Particle& pip = LAMBDAC.decayProducts()[ix].at(sign * PID::PIPLUS)[0];
        _h[0]->fill((pip.momentum() + eta.momentum()).mass());
        _h[1]->fill((lam.momentum() + pip.momentum()).mass());
        _h[2]->fill((lam.momentum() + eta.momentum()).mass());
      }
    }


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

    /// @}


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


  RIVET_DECLARE_PLUGIN(BESIII_2024_I2808543);

}