Rivet analyses

title: BELLE_2007_I686580

Cross section for $e^+e^-\to J/\psi X(3940)$ at $\sqrt{s}=10.6\,$GeV

Experiment: BELLE (KEKB)

Inspire ID: 686580

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 98 (2007) 082001

Beams: e+ e-

Beam energies: (5.3, 5.3)GeV

Run details: - e+e- -> J/psi X(3940)

Cross section for $e^+e^-\to J/\psi X(3940)$ at $\sqrt{s}=10.6\,$GeV. The $X(3940)$ is measure in modes with more than two charged tracks. The status of the $X(3940)$ is not clear, we take the PDG code to be 9010441, which can be changed using the PID option

Source code:BELLE_2007_I686580.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- > J/psi X(3940) class BELLE_2007_I686580 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2007_I686580);


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

/// Book histograms and initialise projections before the run
void init() {
  // set the PDG code
  _pid = getOption<int>("PID", 9010441);
  // projections
  declare("FS", FinalState());
  declare("UFS", UnstableParticles(Cuts::pid == 443 || Cuts::pid == _pid));
  // histograms
  book(_h, 1, 1, 1);
}

void findChildren(const Particle& p, map<long, int>& nRes, int& ncount, unsigned int& nCharged) {
  for (const Particle& child : p.children()) {
    if (child.children().empty()) {
      --nRes[child.pid()];
      --ncount;
      if (PID::isCharged(p.pid())) ++nCharged;
    }
    else {
      findChildren(child, nRes, ncount, nCharged);
    }
  }
}

/// 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;
  }
  // loop over J/psi
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  bool matched = false;
  for (const Particle& p : ufs.particles(Cuts::pid == 443)) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    unsigned int nCharged = 0;
    findChildren(p, nRes, ncount, nCharged);
    // X(3940)
    for (const Particle& p2 : ufs.particles(Cuts::pid == _pid)) {
      map<long, int> nResB = nRes;
      int ncountB = ncount;
      unsigned int nChargedB = 0;
      findChildren(p2, nResB, ncountB, nChargedB);
      if (ncountB != 0) continue;
      matched = true;
      for (const auto& val : nResB) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        if (nCharged > 2) _h->fill("10.6"s);
        break;
      }
    }
    if (matched) break;
  }
}


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

/// @}


/// @name Histograms
/// @{
int _pid;
BinnedHistoPtr<string> _h;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2007_I686580);

} ```