Rivet analyses

title: BESIII_2023_I2643786

Cross section for $e^+e^-\to\omega\pi^+\pi^-$ between 4 and 4.6 GeV

Experiment: BESIII (BEPC)

Inspire ID: 2643786

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2303.09718

Beams: e+ e-

Beam energies: ANY

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to\omega\pi^+\pi^-$ between 4 and 4.6 GeV by the BESIII collaboration. The cross section for a number of resonant intermediate states are also measured.

Source code:BESIII_2023_I2643786.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- -> omega pi+ pi- class BESIII_2023_I2643786 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2643786);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  for (unsigned int ix = 0; ix < 7; ++ix) {
    book(_n[ix], "TMP/n_" + toString(ix + 1));
  }
}

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;
  }
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  bool hasOmegaPiPi = false, hasResonance = false;
  for (const Particle& p : ufs.particles(Cuts::pid == 223)) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    // first the omega pi pi final state
    if (ncount == 2) {
      hasOmegaPiPi = true;
      for (const auto& val : nRes) {
        if (abs(val.first) == 211) {
          if (val.second != 1) {
            hasOmegaPiPi = false;
            break;
          }
        }
        else if (val.second != 0) {
          hasOmegaPiPi = false;
          break;
        }
      }
      if (hasOmegaPiPi) _n[0]->fill();
    }
    if (!hasOmegaPiPi) continue;
    // now omega + second resonance
    for (const Particle& p2 : ufs.particles(Cuts::pid == 9000221 || Cuts::pid == 9010221
                                            || Cuts::pid == 10221 || Cuts::pid == 225)) {
      if (p2.children().empty()) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(p2, nRes2, ncount2);
      hasResonance = true;
      if (ncount2 != 0) continue;
      for (const auto& val : nRes2) {
        if (val.second != 0) {
          hasResonance = false;
          break;
        }
      }
      if (hasResonance) {
        if (p2.pid() == 9000221)
          _n[1]->fill();
        else if (p2.pid() == 9010221)
          _n[2]->fill();
        else if (p2.pid() == 10221)
          _n[3]->fill();
        else if (p2.pid() == 225)
          _n[4]->fill();
        break;
      }
    }
    if (hasOmegaPiPi) break;
  }
  if (hasResonance || !hasOmegaPiPi) return;
  // b_1 pi
  for (const Particle& p : ufs.particles(Cuts::abspid == 10213 || 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 ipi = -p.pid() / p.abspid() * 211;
    hasResonance = true;
    for (const auto& val : nRes) {
      if (val.first == ipi) {
        if (val.second != 1) {
          hasOmegaPiPi = false;
          break;
        }
      }
      else if (val.second != 0) {
        hasResonance = false;
        break;
      }
    }
    if (hasResonance) {
      if (p.abspid() == 10213)
        _n[5]->fill();
      else
        _n[6]->fill();
      break;
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 7; ++ix) {
    scale(_n[ix], crossSection() / sumOfWeights() / picobarn);
    unsigned int ih = 2, iy = ix;
    if (ix == 0) {
      ih = 1;
      iy = 1;
    }
    Estimate1DPtr mult;
    book(mult, ih, 1, iy);
    for (auto& b : mult->bins()) {
      if (inRange(sqrtS() / GeV, b.xMin(), b.xMax())) {
        b.set(_n[ix]->val(), _n[ix]->err());
      }
    }
  }
}

/// @}


/// @name Histograms
/// @{
CounterPtr _n[7];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2023_I2643786);

} ```