Rivet analyses

title: BABAR_2006_I722213

Mass distributions in $\Lambda_c^+\to \Lambda\bar{K}^0K^+$

Experiment: BABAR (PEP-II)

Inspire ID: 722213

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - hep-ex/0607043 [hep-ex]

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c+ mesons

Measurement of the mass distributions in the decay $\Lambda_c^+\to \Lambda\bar{K}^0K^+$, together with angular distributions in the $\Xi(1690)$ region. The data were read from the plots in the paper but have been corrected for efficiency/acceptance but not resolution.

Source code:BABAR_2006_I722213.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Lambda_c+ -> Lambda Kbar0 K+ class BABAR_2006_I722213 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2006_I722213);


/// @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::LAMBDA);
  LAMBDAC.addStable(-PID::LAMBDA);
  declare(LAMBDAC, "LAMBDAC");
  // histograms
  for (size_t ix = 0; ix < 3; ++ix) {
    book(_h_mass[ix], 1, 1, 1 + ix);
  }
  for (size_t ix = 0; ix < 2; ++ix) {
    book(_h_ctheta[ix], 2, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{PID::LAMBDA, 1}, {321, 1}, {310, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-PID::LAMBDA, 1}, {-321, 1}, {310, 1}};
  DecayedParticles LAMBDAC = apply<DecayedParticles>(event, "LAMBDAC");
  // loop over particles
  for (size_t 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 Particle& lam = LAMBDAC.decayProducts()[ix].at(sign * PID::LAMBDA)[0];
    const Particle& K0 = LAMBDAC.decayProducts()[ix].at(310)[0];
    const Particle& Kp = LAMBDAC.decayProducts()[ix].at(sign * 321)[0];
    double mLamK = (lam.mom() + K0.mom()).mass();
    _h_mass[0]->fill(mLamK);
    _h_mass[1]->fill((Kp.mom() + K0.mom()).mass() - Kp.mass() - K0.mass());
    _h_mass[2]->fill((lam.mom() + Kp.mom()).mass() - Kp.mass() - lam.mass());
    // take Xi(1690) to be any resonance in mass region
    if (mLamK < 1.6725 || mLamK > 1.6975) continue;
    if (LAMBDAC.decaying()[ix].children().size() != 2) continue;
    if (LAMBDAC.decaying()[ix].children()[0].abspid() != 321
        && LAMBDAC.decaying()[ix].children()[1].abspid() != 321)
      continue;
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        LAMBDAC.decaying()[ix].mom().betaVec());
    FourMomentum pbaryon1 = boost1.transform(LAMBDAC.decaying()[ix].mom());
    FourMomentum pbaryon2 = boost1.transform(lam.mom());
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pbaryon1.betaVec());
    Vector3 axis = pbaryon1.p3().unit();
    FourMomentum pp = boost2.transform(pbaryon2);
    // calculate angle
    double cTheta = pp.p3().unit().dot(axis);
    _h_ctheta[0]->fill(cTheta);
    _h_ctheta[1]->fill(cTheta);
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_mass[3];
Histo1DPtr _h_ctheta[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2006_I722213);

} ```