Rivet analyses

title: BABAR_2021_I1938254

Cross sections for $e^+e^-\to\pi^+\pi^-4\pi^0$ and $e^+e^-\to\pi^+\pi^-3\pi^0\eta$ between threshold and 4.5 GeV

Experiment: BABAR (PEP-II)

Inspire ID: 1938254

Status: VALIDATED

Authors: - Peter Richardson

References: - 2110.00823

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Cross sections for $e^+e^-\to\pi^+\pi^-4\pi^0$ and $e^+e^-\to\pi^+\pi^-3\pi^0\eta$ between threshold and 4.5 GeV measured by BaBar using radiative return. The contributions of the $\eta\pi^+\pi^-\pi^0$, $\eta\omega$, $\omega\pi^0\pi^0\pi^0$ intermediate states are also measured. Useful to compare hadronization and other non-perturbative models at low energies between 1.4 and 4.5 GeV.

Source code:BABAR_2021_I1938254.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- > pi+pi-4pi0 and pi+pi-3pi0 eta class BABAR_2021_I1938254 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2021_I1938254);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  // Histograms
  for (unsigned int ix = 0; ix < 5; ++ix) {
    book(_num[ix], "TMP/num_" + to_string(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) {
  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;
  }
  // stable final state
  if (nCount[211] == 1 && nCount[-211] == 1 && nCount[111] == 4) _num[0]->fill();
  // intermediate states
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::pid == 221 || Cuts::pid == 223)) {
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    // eta +X
    int idOther;
    if (p.pid() == 221) {
      idOther = 223;
      bool matched = true;
      for (const auto& val : nRes) {
        if (abs(val.first) == 211 || val.first == -211) {
          if (val.second != 1) {
            matched = false;
            break;
          }
        }
        else if (val.first == 111) {
          // 1 or 3 pi0
          if (val.second != 3 && val.second != 1) {
            matched = false;
            break;
          }
        }
        else if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        if (nRes[111] == 1)
          _num[1]->fill();
        else
          _num[4]->fill();
      }
    }
    // omega+X
    else {
      idOther = 221;
      // omega+ 3pi0
      bool matched = true;
      for (const auto& val : nRes) {
        if (abs(val.first) == 111) {
          if (val.second != 3) {
            matched = false;
            break;
          }
        }
        else if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        _num[3]->fill();
      }
    }
    for (const Particle& p2 : ufs.particles(Cuts::pid == idOther)) {
      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) {
        _num[2]->fill();
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / nanobarn / sumOfWeights();
  for (unsigned int ix = 0; ix < 5; ++ix) {
    double sigma = _num[ix]->val() * fact;
    double error = _num[ix]->err() * fact;
    Estimate1DPtr mult;
    book(mult, 1 + ix, 1, 1);
    for (auto& b : mult->bins()) {
      if (inRange(sqrtS() / GeV, b.xMin(), b.xMax())) {
        b.set(sigma, error);
      }
    }
  }
}

///@}


/// @name Histograms
///@{
CounterPtr _num[5];
///@}

};

RIVET_DECLARE_PLUGIN(BABAR_2021_I1938254);

} ```