Rivet analyses

title: SND_2019_I1726419

Cross section for $e^+e^-\to\pi^+\pi^-\pi^0\eta$ for energies below 2 GeV

Experiment: SND (VEPP-2M)

Inspire ID: 1726419

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1903.09307

Beams: e+ e-

Beam energies: (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.8, 0.8); (0.8, 0.8); (0.8, 0.8); (0.8, 0.8); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (1.0, 1.0); (1.0, 1.0)GeV

Run details: - e+ e- to hadrons

Measurement of the cross section for $e^+e^-\to\pi^+\pi^-\pi^0\eta$, and the resonant sub-processes $\omega\eta$, $\phi\eta$ and $a_0(980)\rho$, for energies below 2 GeV by the SND experiment.

Source code:SND_2019_I1726419.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief SND pi+pi-pi0eta cross section class SND_2019_I1726419 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(SND_2019_I1726419);


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

/// Book histograms and initialise projections before the run
void init() {

  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  for (size_t ix = 0; ix < 4; ++ix) {
    book(_sigma[ix], 1, 1, 1 + ix);
  }
  for (const string& en : _sigma[0].binning().edges<0>()) {
    double eval = stod(en) * GeV;
    if (isCompatibleWithSqrtS(eval)) {
      _sqs = en;
      break;
    }
  }
  raiseBeamErrorIf(_sqs.empty());
}


void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) const {
  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) {

  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");
  bool found = false, foundOmegaPhi = false;
  for (const Particle& p : ufs.particles(Cuts::pid == 221)) {
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    // eta pi+pi-
    if (ncount == 3) {
      bool matched = true;
      for (const auto& val : nRes) {
        if (abs(val.first) == 211 || val.first == 111) {
          if (val.second != 1) {
            matched = false;
            break;
          }
        }
        else if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        _sigma[0]->fill(_sqs);
        found = true;
      }
    }
    for (const Particle& p2 : ufs.particles()) {
      if (p2.pid() != 223 && p2.pid() != 333) continue;
      map<long, int> nResB = nRes;
      int ncountB = ncount;
      findChildren(p2, nResB, ncountB);
      if (ncountB != 0) continue;
      bool matched2 = true;
      for (const auto& val : nResB) {
        if (val.second != 0) {
          matched2 = false;
          break;
        }
      }
      if (matched2) {
        if (p2.pid() == 223) {
          _sigma[1]->fill(_sqs);
        }
        else if (p2.pid() == 333 && sqrtS() > 1.6 * GeV) {
          _sigma[2]->fill(_sqs);
        }
        foundOmegaPhi = true;
      }
    }
  }
  if (found && !foundOmegaPhi) _sigma[3]->fill(_sqs);
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_sigma, crossSection() / nanobarn / sumOfWeights());
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _sigma[4];
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(SND_2019_I1726419); } ```