Rivet analyses

Cross section for e+e− → ωπ0 → π+π−π0π0 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− → ωπ0 → π+π−π0π0 for $\sqrt{s}=1.05\to2$ GeV by the SND collaboration.

Source code:SND_2023_I2693057.cc

// -*- 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);
}