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/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.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);

}