Rivet analyses

Kinematic distributions in Λc+ → Λ0e+νe

Experiment: BESIII (BEPC)

Inspire ID: 2127373

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2207.14149

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c+

Measurement of the kinematic distributions in Λc+ → Λ0e+νe by BES-III. N.B. The data were read from the paper and may not have been corrected for acceptance.

Source code:BESIII_2022_I2127373.cc

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

namespace Rivet {


  /// @brief Lambda_c+ -> Lambda0 e+ nu_e
  class BESIII_2022_I2127373 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2127373);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 4122);
      declare(ufs, "UFS");
      DecayedParticles LAMBDAC(ufs);
      LAMBDAC.addStable(PID::PI0);
      LAMBDAC.addStable(PID::K0S);
      LAMBDAC.addStable(PID::ETA);
      LAMBDAC.addStable(PID::ETAPRIME);
      declare(LAMBDAC, "LAMBDAC");

      // Book histograms
      for (unsigned int ix = 0; ix < 4; ++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 = {{2212, 1}, {-211, 1}, {-11, 1}, {12, 1}};
      DecayedParticles LAMBDAC = apply<DecayedParticles>(event, "LAMBDAC");
      // loop over particles
      for (unsigned int ix = 0; ix < LAMBDAC.decaying().size(); ++ix) {
        if (!LAMBDAC.modeMatches(ix, 4, mode)) continue;
        const Particle& pp = LAMBDAC.decayProducts()[ix].at(2212)[0];
        const Particle& pim = LAMBDAC.decayProducts()[ix].at(-211)[0];
        const Particle& ep = LAMBDAC.decayProducts()[ix].at(-11)[0];
        const Particle& nue = LAMBDAC.decayProducts()[ix].at(12)[0];
        if (LAMBDAC.decaying()[ix].children(Cuts::pid == PID::LAMBDA).empty()) continue;
        FourMomentum pLambda = pp.momentum() + pim.momentum();
        FourMomentum qq = LAMBDAC.decaying()[ix].momentum() - pLambda;
        _h[0]->fill(qq.mass2());
        // boost momenta to LAMBDAC rest frame
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
            LAMBDAC.decaying()[ix].momentum().betaVec());
        FourMomentum pLam = boost.transform(pLambda);
        Matrix3 ptoz(-pLam.p3().unit(), Vector3(0, 0, 1));
        boost.preMult(ptoz);
        // the momenta in frane to W along z
        FourMomentum pD = boost.transform(LAMBDAC.decaying()[ix].momentum());
        FourMomentum pP = boost.transform(pp.momentum());
        FourMomentum ppi = boost.transform(pim.momentum());
        FourMomentum pe = boost.transform(ep.momentum());
        FourMomentum pnu = boost.transform(nue.momentum());
        pLambda = pP + ppi;
        qq = pD - pLambda;
        LorentzTransform boostL = LorentzTransform::mkFrameTransformFromBeta(pLambda.betaVec());
        Vector3 axisP = boostL.transform(pP).p3().unit();
        _h[1]->fill(axisP.dot(pLambda.p3().unit()));
        LorentzTransform boostW = LorentzTransform::mkFrameTransformFromBeta(qq.betaVec());
        Vector3 axisE = boostW.transform(pe).p3().unit();
        _h[2]->fill(-axisE.dot(qq.p3().unit()));
        axisP.setZ(0.);
        axisE.setZ(0.);
        double chi = atan2(axisE.cross(axisP).dot(qq.p3().unit()), axisE.dot(axisP));
        _h[3]->fill(chi);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 4; ++ix) normalize(_h[ix]);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[4];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2127373);

}