Rivet analyses

title: BESIII_2020_I1795949

Cross section for $e^+e^-\to D_s^{(*)+}D_{s1}(2460)^-+\text{c.c.}$

Experiment: BESIII (BEPC)

Inspire ID: 1795949

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv 2005.05850

Beams: e+ e-

Beam energies: (2.2, 2.2); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to D_s^{(*)+}D_{s1}(2460)^-+\text{c.c.}$ by the BESIII experiment for centre-of-mass energies between 4.467 and 4.6 GeV.

Source code:BESIII_2020_I1795949.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- -> Ds(*) D_s1 class BESIII_2020_I1795949 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1795949);


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

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

  // Book histograms
  book(_c_Ds, 1, 1, 1);
  book(_c_DsStar, 2, 1, 1);
  for (const string& en : _c_Ds.binning().edges<0>()) {
    const double eval = stod(en);
    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()] -= 1;
      --ncount;
    }
    else {
      findChildren(child, nRes, ncount);
    }
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  const FinalState& fs = apply<FinalState>(event, "FS");
  // total analyse final state
  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  // unstable charm analysis
  Particles ds = apply<UnstableParticles>(event, "UFS")
                     .particles(Cuts::abspid == 431 or Cuts::abspid == 433 or Cuts::abspid == 20433);
  for (size_t ix = 0; ix < ds.size(); ++ix) {
    const Particle& p1 = ds[ix];
    int id1 = abs(p1.pid());
    // check fs
    bool fs = true;
    for (const Particle& child : p1.children()) {
      if (child.pid() == p1.pid()) {
        fs = false;
        break;
      }
    }
    if (!fs) continue;
    // find the children
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p1, nRes, ncount);
    bool matched = false;
    int sign = p1.pid() / id1;
    // loop over the other fs particles
    for (size_t iy = ix + 1; iy < ds.size(); ++iy) {
      const Particle& p2 = ds[iy];
      fs = true;
      for (const Particle& child : p2.children()) {
        if (child.pid() == p2.pid()) {
          fs = false;
          break;
        }
      }
      if (!fs) continue;
      if (p2.pid() / abs(p2.pid()) == sign) continue;
      int id2 = abs(p2.pid());
      if (!p2.parents().empty() && p2.parents()[0].pid() == p1.pid()) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(p2, nRes2, ncount2);
      if (ncount2 != 0) continue;
      matched = true;
      for (const auto& val : nRes2) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        if ((id1 == 431 && id2 == 20433) || (id1 == 20433 && id2 == 421)) {
          _c_Ds->fill(_sqs);
        }
        else if ((id1 == 433 && id2 == 20433) || (id1 == 20433 && id2 == 433)) {
          _c_DsStar->fill(_sqs);
        }
        break;
      }
    }
    if (matched) break;
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / sumOfWeights() / picobarn;
  scale(_c_Ds, fact);
  scale(_c_DsStar, fact);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _c_Ds, _c_DsStar;
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2020_I1795949);

} ```