Rivet analyses

title: BELLE_2006_I727063

$\gamma\gamma\to\Lambda\bar{\Lambda}^0$ and $\Sigma^0\bar{\Sigma}^0$ for $\sqrt{s}=2.35\to3.8\,$GeV

Experiment: BELLE (KEKB)

Inspire ID: 727063

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - hep-ex/0609048 [hep-ex]

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma -> hadrons

$\gamma\gamma\to\Lambda\bar{\Lambda}^0$ and $\Sigma^0\bar{\Sigma}^0$ for $\sqrt{s}=2.35\to3.8\,$GeV''

Source code:BELLE_2006_I727063.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief gamma gamma -> Lambda Lmabdabar, Sigma0 Sigmabar0 class BELLE_2006_I727063 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2006_I727063);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(Cuts::abspid == 3122 || Cuts::abspid == 3212), "UFS");
  // histograms
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_sigma[ix], "TMP/c_" + toString(ix + 1), refData(1, 1, 1 + ix));
  }
}

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

/// Perform the per-event analysis
void analyze(const Event& event) {
  // check the final state
  const FinalState& fs = apply<FinalState>(event, "FS");
  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  Particle Lambda, Lambar;
  // loop over baryon
  bool matched = false;
  for (const Particle& p : ufs.particles()) {
    if (p.children().empty() || p.pid() < 0) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    // and antibaryons
    for (const Particle& p2 : ufs.particles()) {
      if (p2.children().empty() || p2.pid() > 0) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(p2, nRes2, ncount2);
      if (ncount2 != 0) continue;
      matched = 2;
      for (const auto& val : nRes2) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        Lambda = p;
        Lambar = p2;
        break;
      }
    }
  }
  if (!matched) vetoEvent;
  if (Lambda.pid() != -Lambar.pid()) vetoEvent;
  double cTheta = abs(Lambda.momentum().z() / Lambda.momentum().p3().mod());
  if (cTheta > 0.6) vetoEvent;
  if (Lambda.pid() == 3122)
    _sigma[1]->fill(sqrtS());
  else
    _sigma[0]->fill(sqrtS());
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / nanobarn / sumOfWeights();
  for (unsigned int ix = 0; ix < 2; ++ix) {
    scale(_sigma[ix], fact);
    Estimate1DPtr tmp;
    book(tmp, 1, 1, 1 + ix);
    barchart(_sigma[ix], tmp);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _sigma[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2006_I727063);

} ```