Rivet analyses

title: BESIII_2022_I2127373

Kinematic distributions in $\Lambda_c^+\to \Lambda^0 e^+\nu_e$

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 $\Lambda_c^+\to \Lambda^0 e^+\nu_e$ 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++ // -- 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);

} ```