Rivet analyses

title: SND_2020_I1809286

Cross section for $e^+e^-\to\pi^+\pi^-\pi^0$ between 1.15 and 2 GeV

Experiment: SND (VEPP-2000)

Inspire ID: 1809286

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 2007.14595

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Cross section for $e^+e^-\to\pi^+\pi^-\pi^0$ between 1.15 and 2 GeV measured by SND. The $\omega\pi^0$, $\rho\pi$ and $\rho(1450)\pi$ subprocesses are also extracted.

Source code:SND_2020_I1809286.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- > pi+pi-pi0 class SND_2020_I1809286 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(SND_2020_I1809286);


/// @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 < 2; ++ix) {
    book(_sigma_total[ix], 1 + ix, 1, 1);
    for (const string& en : _sigma_total[ix].binning().edges<0>()) {
      double eval = stod(en) * GeV;
      if (isCompatibleWithSqrtS(eval, 5e-3)) {
        _sqs[ix] = en;
        break;
      }
    }
  }
  raiseBeamErrorIf(_sqs[0].empty() && _sqs[1].empty() && !inRange(sqrtS() / GeV, 1.15, 2.));
  for (size_t ix = 0; ix < 3; ++ix) {
    book(_sigma_res[ix], "/TMP/c_res_" + toString(ix), refData(3, 1, 1 + ix));
  }
  book(_h_x[0], 4, 1, 1);
  book(_h_m[0], 4, 1, 3);
  book(_h_x[1], 4, 1, 2);
  book(_h_m[1], 4, 1, 4);
}

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);
  Particle pip, pim;
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
    if (p.pid() == 211)
      pip = p;
    else if (p.pid() == -211)
      pim = p;
  }
  if (ntotal != 3) vetoEvent;
  if (nCount[-211] == 1 && nCount[211] == 1 && nCount[111] == 1) {
    _sigma_total[0]->fill(_sqs[0]);
    _sigma_total[1]->fill(_sqs[1]);
  }
  else
    vetoEvent;
  if (inRange(sqrtS() / GeV, 1.42, 1.48)) {
    _h_x[0]->fill(pip.p() / sqrtS());
    _h_x[0]->fill(pim.p() / sqrtS());
    _h_m[0]->fill((pip.mom() + pim.mom()).mass() / MeV);
  }
  else if (inRange(sqrtS() / GeV, 1.65, 1.68)) {
    _h_x[1]->fill(pip.p() / sqrtS());
    _h_x[1]->fill(pim.p() / sqrtS());
    _h_m[1]->fill((pip.mom() + pim.mom()).mass() / MeV);
  }
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::abspid == 223 || Cuts::abspid == 113 || Cuts::abspid == 213
                                         || Cuts::abspid == 100113 || Cuts::abspid == 100213)) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    if (ncount != 1) continue;
    int idOther = 211;
    if (p.pid() == 223 || p.pid() == 113 || p.pid() == 100113)
      idOther = 111;
    else if (p.pid() == 213 || p.pid() == 100213)
      idOther = -211;
    bool matched = true;
    for (const auto& val : nRes) {
      if (val.first == idOther) {
        if (val.second != 1) {
          matched = false;
          break;
        }
      }
      else if (val.second != 0) {
        matched = false;
        break;
      }
    }
    if (!matched) continue;
    if (matched) {
      if (p.pid() == 223)
        _sigma_res[2]->fill(sqrtS());
      else if (p.pid() == 213 || p.pid() == 113) {
        _sigma_res[0]->fill(sqrtS());
      }
      else
        _sigma_res[1]->fill(sqrtS());
      break;
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_x, 1.0, false);
  normalize(_h_m, 1.0, false);
  const double fact = crossSection() / nanobarn / sumOfWeights();
  scale(_sigma_total, fact);
  for (size_t ix = 0; ix < 3; ++ix) {
    scale(_sigma_res[ix], fact);
    Estimate1DPtr tmp;
    book(tmp, 3, 1, 1 + ix);
    barchart(_sigma_res[ix], tmp);
  }
}

/// @}


/// @name Histograms
/// @{
string _sqs[2];
Histo1DPtr _sigma_res[3];
Histo1DPtr _h_x[2], _h_m[2];
BinnedHistoPtr<string> _sigma_total[2];
/// @}

};

RIVET_DECLARE_PLUGIN(SND_2020_I1809286); } ```