Rivet analyses

title: BABAR_2007_I760730

Cross section for $e^+e^-\to\Lambda\bar{\Lambda}$, $\Sigma^0\bar{\Sigma}^0$ and $\Lambda\bar{\Sigma}^0$ between threshold and 3 GeV

Experiment: BABAR (PEP-II)

Inspire ID: 760730

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D76 (2007) 092006

Beams: e+ e-

Beam energies: ANY

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to\Lambda\bar{\Lambda}$ between threshold and 3 GeV.

Source code:BABAR_2007_I760730.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- > hyperons class BABAR_2007_I760730 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2007_I760730);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  book(_nLL, "/TMP/nLL");
  book(_nSS, "/TMP/nSS");
  book(_nLS, "/TMP/nLS");
}

void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
  for (const Particle& child : p.children()) {
    if (child.children().empty()) {
      nRes[child.pid()] -= 1;
      --ncount;
    }
    else
      findChildren(child, nRes, ncount);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  const FinalState& fs = apply<FinalState>(event, "FS");
  // total hadronic and muonic cross sections
  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }

  // find the Lambdas and Sigmas
  const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
  for (unsigned int ix = 0; ix < ufs.particles().size(); ++ix) {
    const Particle& p1 = ufs.particles()[ix];
    if (abs(p1.pid()) != 3122 && abs(p1.pid()) != 3212) continue;
    bool matched = false;
    // check fs
    bool fs = true;
    for (const Particle& child : p1.children()) {
      if (child.pid() == p1.pid()) {
        fs = false;
        break;
      }
    }
    if (!fs) continue;
    // find the children
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p1, nRes, ncount);
    for (unsigned int iy = ix + 1; iy < ufs.particles().size(); ++iy) {
      const Particle& p2 = ufs.particles()[iy];
      if (abs(p2.pid()) != 3122 && abs(p2.pid()) != 3212) continue;
      // check fs
      bool fs = true;
      for (const Particle& child : p2.children()) {
        if (child.pid() == p2.pid()) {
          fs = false;
          break;
        }
      }
      if (!fs) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(p2, nRes2, ncount2);
      if (ncount2 != 0) continue;
      matched = true;
      for (const auto& val : nRes2) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        if (abs(p1.pid()) == 3122 && abs(p2.pid()) == 3122)
          _nLL->fill();
        else if (abs(p1.pid()) == 3212 && abs(p2.pid()) == 3212)
          _nSS->fill();
        else
          _nLS->fill();
        break;
      }
    }
    if (matched) break;
  }
}

/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / sumOfWeights() / picobarn;
  for (unsigned int ix = 1; ix < 4; ++ix) {
    double sigma, error;
    if (ix == 1) {
      sigma = _nLL->val() * fact;
      error = _nLL->err() * fact;
    }
    else if (ix == 2) {
      sigma = _nSS->val() * fact;
      error = _nSS->err() * fact;
    }
    else {
      sigma = _nLS->val() * fact;
      error = _nLS->err() * fact;
    }
    Estimate1DPtr mult;
    book(mult, ix, 1, 1);
    for (auto& b : mult->bins()) {
      if (inRange(sqrtS() / GeV, b.xMin(), b.xMax())) {
        b.set(sigma, error);
      }
    }
  }
}

/// @}


/// @name Histograms
/// @{
CounterPtr _nLL, _nSS, _nLS;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2007_I760730);

} ```