Rivet analyses

title: MD1_1994_I362599

$\Lambda^0$ production at $\Upsilon(1S)$ and nearby $e^+e^-$ continuum

Experiment: MD1 (VEPP-4)

Inspire ID: 362599

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys.C 62 (1994) 367-370

Beams: e+ e-

Beam energies: ANY

Run details: - e+e- > hadrons at Upslion(1S) and 10.49 GeV

Spectra for $\Lambda^0$ and rates for $\Lambda^0$ and $\Xi^-$ production in $\Upsilon(1S)$ decay and $\Lambda^0$ production rate in the nearby continuum.

Source code:MD1_1994_I362599.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Lambda in Upsilon(1S) decay and nearby continuum class MD1_1994_I362599 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(MD1_1994_I362599);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  declare(UnstableParticles(), "UFS");
  // histos
  book(_weightSum_cont, "TMP/weightSumcont");
  book(_weightSum_Ups1, "TMP/weightSumUps1");
  book(_h_spect, 1, 1, 1);
  for (unsigned int ix = 0; ix < 2; ++ix) {
    for (unsigned int iy = 0; iy < 2; ++iy) {
      book(_mult[ix][iy], "/TMP/MULT_" + toString(ix) + "_" + toString(iy));
    }
  }
}

/// Recursively walk the decay tree to find decay products of @a p
void findDecayProducts(Particle mother, Particles& unstable) {
  for (const Particle& p : mother.children()) {
    const int id = p.abspid();
    if (id == PID::LAMBDA || id == PID::XIMINUS) unstable.push_back(p);
    if (!p.children().empty()) findDecayProducts(p, unstable);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // Find the upsilons
  // First in unstable final state
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  Particles upsilons = ufs.particles(Cuts::pid == 553);
  // continuum
  if (upsilons.empty()) {
    _weightSum_cont->fill();
    // Unstable particles
    size_t nLam = ufs.particles(Cuts::abspid == PID::LAMBDA).size();
    _mult[1][0]->fill(nLam);
  }
  else {
    for (const Particle& ups : upsilons) {
      _weightSum_Ups1->fill();
      Particles unstable;
      LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
      // Find the decay products we want
      findDecayProducts(ups, unstable);
      for (const Particle& p : unstable) {
        int id = p.abspid();
        if (id == PID::LAMBDA) {
          double xp = 2. * boost.transform(p.momentum()).p3().mod() / ups.mass();
          _h_spect->fill(xp);
          _mult[0][0]->fill();
        }
        else if (id == PID::XIMINUS) {
          _mult[0][1]->fill();
        }
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  if (_weightSum_Ups1->val() > 0.) {
    scale(_h_spect, 1. / *_weightSum_Ups1);
    for (size_t iy = 0; iy < 2; ++iy) {
      BinnedEstimatePtr<string> est;
      book(est, 2 + iy * 2, 1, 1);
      if (_weightSum_Ups1->val() > 0.) {
        scale(_mult[0][iy], 1. / *_weightSum_Ups1);
        est->bin(1).set(_mult[0][iy]->val(), _mult[0][iy]->err());
      }
    }
  }
  if (_weightSum_cont->val() > 0.) {
    scale(_mult[1][0], 1. / *_weightSum_cont);
    Estimate1DPtr est;
    book(est, 3, 1, 1);
    est->bin(1).set(_mult[1][0]->val(), _mult[1][0]->err());
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_spect;
CounterPtr _weightSum_cont, _weightSum_Ups1;
CounterPtr _mult[2][2];
/// @}

};

RIVET_DECLARE_PLUGIN(MD1_1994_I362599);

} ```