Rivet analyses

title: SND_2023_I2693057

Cross section for $e^+e^-\to\omega\pi^0\to\pi^+\pi^-\pi^0\pi^0$ for $\sqrt{s}=1.05\to2$ GeV

Experiment: SND (VEPP-2M)

Inspire ID: 2693057

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2309.00280

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons, pi0 set stable

Measurement of the cCross section for $e^+e^-\to\omega\pi^0\to\pi^+\pi^-\pi^0\pi^0$ for $\sqrt{s}=1.05\to2$ GeV by the SND collaboration.

Source code:SND_2023_I2693057.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+ e- > omega pi0 -> 4pi class SND_2023_I2693057 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(SND_2023_I2693057);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(Cuts::pid == 223), "UFS");
  book(_nOmegaPi, 1, 1, 1);
  for (const string& en : _nOmegaPi.binning().edges<0>()) {
    double eval = stod(en) * MeV;
    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) {
  // 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;
  }
  // require 4 pi final state
  if (ntotal != 4) vetoEvent;
  if (nCount[211] != 1 || nCount[-211] != 1 || nCount[111] != 2) vetoEvent;
  // omega
  for (const Particle& p : apply<FinalState>(event, "UFS").particles()) {
    if (p.children().empty()) continue;
    // find the omega
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    // omega pi0
    if (ncount != 1) continue;
    bool matched = true;
    for (const auto& val : nRes) {
      if (val.first == 111) {
        if (val.second != 1) {
          matched = false;
          break;
        }
      }
      else if (val.second != 0) {
        matched = false;
        break;
      }
    }
    if (matched) {
      _nOmegaPi->fill(_sqs);
      break;
    }
  }
}


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

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _nOmegaPi;
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(SND_2023_I2693057); } ```