Rivet analyses

title: CMD3_2017_I1606078

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

Experiment: CMD3 (VEPP-2M)

Inspire ID: 1606078

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1706.06267

Beams: e+ e-

Beam energies: ANY

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 $\omega\eta$and $a_0(980)\rho$, for energies below 2 GeV by the CMD3 experiment

Source code:CMD3_2017_I1606078.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief CMD3 pi+pi-pi0eta cross section class CMD3_2017_I1606078 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMD3_2017_I1606078);


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

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

  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");


  book(_c_all, 1, 1, 1);
  book(_c_omega, 1, 1, 2);
  book(_c_rho, 1, 1, 3);
  book(_c_other, 1, 1, 4);
}

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) {
  // find the final-state particles
  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;
  }
  // find omega/phi + eta
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  bool found = false, foundOmegaPhi = false;
  for (const Particle& p : ufs.particles()) {
    if (p.children().empty()) continue;
    // find the eta
    if (p.pid() != 221) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    // eta pi+pi-pi0
    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) {
        _c_all->fill(round(sqrtS() / MeV));
        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) _c_omega->fill(round(sqrtS() / MeV));
        foundOmegaPhi = true;
      }
    }
  }
  // find a_0 rho
  bool founda0Rho = false;
  for (const Particle& p : ufs.particles()) {
    if (p.children().empty()) continue;
    // find the rho
    if (p.pid() != 113 && abs(p.pid()) != 213) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    int a1id(0);
    if (p.pid() == 213)
      a1id = 9000211;
    else if (p.pid() == -213)
      a1id = -9000211;
    else
      a1id = 9000111;
    for (const Particle& p2 : ufs.particles()) {
      if (p2.pid() != a1id) continue;
      map<long, int> nResB = nRes;
      int ncountB = ncount;
      findChildren(p2, nResB, ncountB);
      if (ncountB != 0) continue;
      bool matched = true;
      for (const auto& val : nResB) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        _c_rho->fill(round(sqrtS() / MeV));
        founda0Rho = true;
        break;
      }
    }
    if (founda0Rho) break;
  }
  if (found && !foundOmegaPhi && !founda0Rho) _c_other->fill(round(sqrtS() / MeV));
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / nanobarn / sumOfWeights();
  scale(_c_all, fact);
  scale(_c_omega, fact);
  scale(_c_rho, fact);
  scale(_c_other, fact);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<int> _c_all, _c_omega, _c_rho, _c_other;
/// @}

};

RIVET_DECLARE_PLUGIN(CMD3_2017_I1606078);

} ```