Rivet analyses

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++ -*-
#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);

}