Rivet analyses

title: BELLE_2010_I841003

Mass distribution in $e^+e^-\to e^+e^- \omega J/\psi$ via $\gamma\gamma\to \omega J\psi$

Experiment: BELLE (KEKB)

Inspire ID: 841003

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 104 (2010) 092001

Beams: e+ e-

Beam energies: (3.5, 8.0)GeV

Run details: - e+ e- > e+e- omega J/psi via photon photon -> omega J/psi

Measurement of the $\omega J/\psi$ mass distribution in $e^+e^-\to e^+e^-\omega J/\psi$ via $\gamma\gamma\to \omega J/\psi$. the data were read from the plots in the paper and may not be corrected for efficiency, although the background givne in the paper has been subtracted.

Source code:BELLE_2010_I841003.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief gamma gamma -> omega J/psi class BELLE_2010_I841003 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2010_I841003);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(Beam(), "Beams");
  declare(FinalState(), "FS");
  declare(UnstableParticles(Cuts::pid == 223 || Cuts::pid == 443), "UFS");
  // histograms
  book(_h, 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()];
      --ncount;
    }
    else {
      findChildren(child, nRes, ncount);
    }
  }
}
bool findScattered(Particle beam, double& q2) {
  bool found = false;
  Particle scat = beam;
  while (!scat.children().empty()) {
    found = false;
    for (const Particle& p : scat.children()) {
      if (p.pid() == scat.pid()) {
        scat = p;
        found = true;
        break;
      }
    }
    if (!found) break;
  }
  if (!found) return false;
  q2 = -(beam.momentum() - scat.momentum()).mass2();
  return true;
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // find scattered leptons and calc Q2
  const Beam& beams = apply<Beam>(event, "Beams");
  double q12 = -1, q22 = -1;
  if (!findScattered(beams.beams().first, q12)) vetoEvent;
  if (!findScattered(beams.beams().second, q22)) vetoEvent;
  // check the final state
  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;
  }
  // find the meson
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p1 : ufs.particles(Cuts::pid == 223)) {
    if (p1.children().empty()) continue;
    bool matched = false;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p1, nRes, ncount);
    for (const Particle& p2 : ufs.particles(Cuts::pid == 443)) {
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(p2, nRes2, ncount2);
      matched = true;
      for (const auto& val : nRes2) {
        if (abs(val.first) == 11) {
          if (val.second != 1) {
            matched = false;
            break;
          }
        }
        else if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        _h->fill((p1.momentum() + p2.momentum()).mass());
        break;
      }
    }
    if (matched) break;
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1.0, false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2010_I841003);

} ```