Rivet analyses

Mass distributions in Λc+ → pKS0π0 and pK−π+

Experiment: BELLE (KEKB)

Inspire ID: 2897384

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 112 (2025) 1, 012013 - arXiv: 2503.04371

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c, originally e+e-

Measurement of the mass distributions in the decay Λc+ → pKS0π0 and pK−π+ by BELLE-II. The data were read from the plots in the paper, are corrected for efficiencies and background subtracted. Resolution may not be corrected.

Source code:BELLE_2025_I2897384.cc

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

namespace Rivet {


  /// @brief Lambda_c+ -> p K pi
  class BELLE_2025_I2897384 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2025_I2897384);


    /// @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);
      declare(LAMBDAC, "LAMBDAC");
      // histograms
      for (size_t ix=0; ix<6; ++ix) {
        book(_h[ix],1,1,1+ix);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode1   = { { PID::PROTON,1}, { 310,1}, { 111,1}};
      static const map<PdgId,unsigned int> & mode1CC = { {-PID::PROTON,1}, { 310,1}, { 111,1}};
      static const map<PdgId,unsigned int> & mode2   = { { PID::PROTON,1}, {-321,1}, { 211,1}};
      static const map<PdgId,unsigned int> & mode2CC = { {-PID::PROTON,1}, { 321,1}, {-211,1}};
      DecayedParticles LAMBDAC = apply<DecayedParticles>(event, "LAMBDAC");
      // loop over particles
      for (size_t ix=0; ix<LAMBDAC.decaying().size(); ++ix) {
        int sign = 1,imode = 0;
        if (LAMBDAC.decaying()[ix].pid()>0 && LAMBDAC.modeMatches(ix,3,mode1)) {
          sign=1;
        }
        else if  (LAMBDAC.decaying()[ix].pid()<0 && LAMBDAC.modeMatches(ix,3,mode1CC)) {
          sign=-1;
        }
        else if (LAMBDAC.decaying()[ix].pid()>0 && LAMBDAC.modeMatches(ix,3,mode2)) {
          sign=1;
          imode=1;
        }
        else if  (LAMBDAC.decaying()[ix].pid()<0 && LAMBDAC.modeMatches(ix,3,mode2CC)) {
          sign=-1;
          imode=1;
        }
        else {
          continue;
        }
        const Particle & pp  = LAMBDAC.decayProducts()[ix].at( sign*PID::PROTON)[0];
        const Particle & pi  = LAMBDAC.decayProducts()[ix].at( imode==0 ? 111 :  sign*211)[0];
        const Particle & KK  = LAMBDAC.decayProducts()[ix].at( imode==0 ? 310 : -sign*321)[0];
        _h[0+imode]->fill((pp.momentum() + KK.momentum()).mass());
        _h[2+imode]->fill((pp.momentum() + pi.momentum()).mass());
        _h[4+imode]->fill((KK.momentum() + pi.momentum()).mass());
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[6];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BELLE_2025_I2897384);

}