Rivet analyses

Mass distributions in Λc+ → Λ0ηπ+

Experiment: BESIII (BEPC)

Inspire ID: 1711896

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 99 (2019) 3, 032010

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c+ mesons

Measurement of the mass distributions in the decay Λc+ → Λ0ηπ+ byt BESIII. The data were read from the plots in the paper, it is not clear that any resolution/efficiency effects have been unfolded.

Source code:BESIII_2019_I1711896.cc

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

namespace Rivet {


  /// @brief Lambda_c+ -> Lambda eta pi+
  class BESIII_2019_I1711896 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1711896);


    /// @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);
      LAMBDAC.addStable(PID::ETAPRIME);
      LAMBDAC.addStable(PID::LAMBDA);
      declare(LAMBDAC, "LAMBDAC");
      // histograms
      book(_h, 1, 1, 1);
      book(_dalitz, "dalitz", 50, 1.5, 3.5, 50, 2.5, 5.0);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{211, 1}, {221, 1}, {PID::LAMBDA, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{-211, 1}, {221, 1}, {-PID::LAMBDA, 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 Particles& lam = LAMBDAC.decayProducts()[ix].at(sign * PID::LAMBDA);
        const Particles& pip = LAMBDAC.decayProducts()[ix].at(sign * PID::PIPLUS);
        const Particles& eta = LAMBDAC.decayProducts()[ix].at(PID::ETA);
        double mLamPi = (lam[0].momentum() + pip[0].momentum()).mass2();
        double mLamEta = (lam[0].momentum() + eta[0].momentum()).mass2();
        _dalitz->fill(mLamPi, mLamEta);
        _h->fill(sqrt(mLamPi));
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h);
      normalize(_dalitz);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h;
    Histo2DPtr _dalitz;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2019_I1711896);

}