Rivet analyses

title: BESIII_2023_I2158340

Ratio of neutral to charged cross sections for $e^+e^-\to \pi\pi\psi_2(3823)$ between 4.23 and 4.70 GeV

Experiment: BESIII (BEPC)

Inspire ID: 2158340

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - JHEP 02 (2023) 171

Beams: * *

Beam energies: ANY

Run details: - e+e- to hadrons, KS0 and pi0 should be set stable

Ratio of the cross section for $e^+e^-\to \pi^0\pi^0\psi_2(3823)$ to that for $e^+e^-\to \pi^+\pi^-\psi_2(3823)$ for centre-of-mass energies between 4.23 and 4.70 GeV.

Source code:BESIII_2023_I2158340.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- > pi pi psi_2 class BESIII_2023_I2158340 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2158340);


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

/// Book histograms and initialise projections before the run
void init() {
  //check CMS energy
  if (!inRange(sqrtS(), 4.23, 4.70)) {
    throw Error("Unexpected sqrtS,must be between 4.23 and 4.70 GeV");
  }
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_n[ix], "TMP/n_" + toString(ix + 1), refData(1, 1, 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()] -= 1;
      --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");
  for (const Particle& chi : ufs.particles(Cuts::pid == 20445)) {
    if (chi.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(chi, nRes, ncount);
    if (ncount != 2) continue;
    if (nRes.find(211) != nRes.end() && nRes.find(-211) != nRes.end() && nRes[211] == 1
        && nRes[-211] == 1) {
      _n[0]->fill(sqrtS());
      break;
    }
    else if (nRes.find(111) != nRes.end() && nRes[111] == 2) {
      _n[1]->fill(sqrtS());
      break;
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  Estimate1DPtr mult;
  book(mult, 1, 1, 1);
  divide(_n[1], _n[0], mult);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _n[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2023_I2158340);

} ```