Rivet analyses

title: BESIII_2020_I1775344

Cross section for $e^+e^-\to K^+K^-\pi^0\pi^0$ from 2.000 to 2.644 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1775344

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 124 (2020) 112001

Beams: e+ e-

Beam energies: (1.0, 1.0); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3)GeV

Run details: - e+e- to hadrons.

Cross section for $e^+e^-\to K^+K^-\pi^0\pi^0$ for centre-of-mass energies from 2.000 to 2.644 GeV measured by BES. The Born cross sections for the subprocesses $e^+e^-\to \phi\pi^0\pi^0$, $K(1460)^+K^-$, $K_1(1400)^+K^-$, $K_1(1270)^+K^-$ and $K^(892)^+K^(892)^-$ are also measured. In addition kinematic distributions are measured at the centre-of-mass energies with the highest integrated luminosity, i.e. 2.125 and 2.396 GeV.

Source code:BESIII_2020_I1775344.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- > K+K- pi0pi0 class BESIII_2020_I1775344 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1775344);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  // histograms
  for (double eVal : allowedEnergies()) {

    const string en = toString(round(eVal / MeV));
    if (isCompatibleWithSqrtS(eVal)) _sqs = en;

    if (en == "2125"s) {
      book(_h[en + "KK"], 7, 1, 1);
      book(_h[en + "pipi"], 7, 1, 2);
      book(_h[en + "Kpi"], 7, 1, 3);
      book(_h[en + "KKpi"], 7, 1, 4);
      book(_h[en + "Kpipi"], 7, 1, 5);
    }
    else if (en == "2396"s) {
      book(_h[en + "KK"], 8, 1, 1);
      book(_h[en + "pipi"], 8, 1, 2);
      book(_h[en + "Kpi"], 8, 1, 3);
      book(_h[en + "KKpi"], 8, 1, 4);
      book(_h[en + "Kpipi"], 8, 1, 5);
    }
  }
  raiseBeamErrorIf(_sqs.empty());

  for (size_t ix = 0; ix < 6; ++ix) {
    book(_c[ix], 1 + ix, 1, 1);
  }
  for (const string& en : _c[0].binning().edges<0>()) {
    const double eval = stod(en);
    if (isCompatibleWithSqrtS(eval)) {
      _edge = en;
      break;
    }
  }
}

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()] -= 1;
      --ncount;
    }
    else {
      findChildren(child, nRes, ncount);
    }
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  const FinalState& fs = apply<FinalState>(event, "FS");
  // find the final-state particles
  map<long, int> nCount;
  int ntotal(0);
  Particles Kp, pi0;
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
    if (p.abspid() == 321)
      Kp += p;
    else if (p.pid() == 111)
      pi0 += p;
  }
  // intermediates
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p :
       ufs.particles(Cuts::abspid == 100321 or Cuts::abspid == 10323 or Cuts::abspid == 20323
                     or Cuts::pid == 333 or Cuts::abspid == 323)) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    // X-/+ with K+/-
    if ((p.abspid() == 100321 || p.abspid() == 10323 || p.abspid() == 20323) && ncount == 1) {
      bool matched = true;
      int Kid = -p.pid() / p.abspid() * 321;
      for (const auto& val : nRes) {
        if (val.first == Kid) {
          if (val.second != 1) {
            matched = false;
            break;
          }
        }
        else if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        if (p.abspid() == 100321)
          _c[2]->fill(_edge);
        else if (p.abspid() == 20323)
          _c[3]->fill(_edge);
        else if (p.abspid() == 10323)
          _c[4]->fill(_edge);
      }
    }
    else if (p.pid() == 333 && ncount == 2) { // phi + 2pi0
      bool matched = true;
      for (const auto& val : nRes) {
        if (val.first == 111) {
          if (val.second != 2) {
            matched = false;
            break;
          }
        }
        else if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) _c[1]->fill(_edge);
    }
    else if (p.abspid() == 323) { // K*K*
      for (const Particle& p2 : ufs.particles(Cuts::pid == -p.pid())) {
        map<long, int> nResB = nRes;
        int ncountB = ncount;
        findChildren(p2, nResB, ncountB);
        if (ncountB != 0) continue;
        bool matched = true;
        for (const auto& val : nResB) {
          if (val.second != 0) {
            matched = false;
            break;
          }
        }
        if (matched) _c[5]->fill(_edge);
      }
    }
  }
  // final-state
  if (ntotal == 4 && nCount[321] == 1 && nCount[-321] == 1 && nCount[111] == 2) {
    _c[0]->fill(_edge);
    if (_sqs == "2125"s || _sqs == "2396"s) {
      FourMomentum pKK = Kp[0].mom() + Kp[1].mom();
      _h[_sqs + "KK"]->fill(pKK.mass());
      FourMomentum pPi = pi0[0].mom() + pi0[1].mom();
      _h[_sqs + "pipi"]->fill(pPi.mass());
      for (size_t ix = 0; ix < 2; ++ix) {
        _h[_sqs + "KKpi"]->fill((pKK + pi0[ix].mom()).mass());
        _h[_sqs + "Kpipi"]->fill((pPi + Kp[ix].mom()).mass());
        for (size_t iy = 0; iy < 2; ++iy) {
          _h[_sqs + "Kpi"]->fill((Kp[ix].mom() + pi0[iy].mom()).mass());
        }
      }
    }
  }
}


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

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _c[6];
map<string, Histo1DPtr> _h;
string _sqs = "", _edge = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2020_I1775344);

} ```